1.
Soybeans are rich in protein. Raw soybeans, however, may contain a trypsin inhibitor. This is a
chemical which prevents the digestion of protein. The presence of this trypsin inhibitor is
genetically controlled. A single gene has alleles TA, TB and TC each of which codes for a
different sort of trypsin inhibitor. These alleles are codominant so plant with the genotype TATB
will produce two sorts of trypsin inhibitor, inhibitor A and inhibitor B. A fourth, recessive allele,
To does not code for a trypsin inhibitor. This information is summarised in the table.
(a)
Allele
Inhibitor produced
TA
A
TB
B
TC
C
To
None
The inheritance of trypsin inhibitors in soybeans is an example of multiple allele
inheritance. Explain how multiple allele inheritance differs from polygenic inheritance.
...................................................................................................................................
...................................................................................................................................
(1)
(b)
(i)
Give all the possible genotypes of a plant which only contains inhibitor A.
...........................................................................................................................
(1)
(ii)
Give all the possible genotypes of the gametes produced by a plant which contains
inhibitors B and C.
...........................................................................................................................
(1)
(c)
Two soybean plants were crossed and the seeds collected and counted. The results are
shown in the table.
Inhibitors present in seed
Number of seeds
A and B
23
A
25
B
48
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(i)
Complete the genetic diagram to explain the results of this cross.
Phenotypes of parents:..................................
.......................................
Genotypes of parents:..................................
.......................................
Genotypes of gametes ......................................................................................
Genotypes of offspring: ....................................................................................
Phenotypes of offspring
Inhibitor A
and
Inhibitor B
Inhibitor A
Inhibitor B
(3)
(ii)
A chi-squared test was applied to the data collected in this investigation. Explain why
statistical tests such as the Chi-squared test should be carried out on data like these.
...........................................................................................................................
...........................................................................................................................
...........................................................................................................................
(2)
Sir George Monoux Sixth Form College
2
An investigation was carried out on the insects living on bean crops. The graph shows the
relationship between the biomass of primary consumers, secondary consumers and producers.
100
Primary
consumers
90
80
70
60
Consumer
–2
biomass/g m
50
40
30
20
Secondary
consumers
10
0
0
200
400
600
Producers biomass/g m
(d)
800
1000
–2
Briefly describe how the data on the biomass of the producers might have been collected.
...................................................................................................................................
...................................................................................................................................
...................................................................................................................................
...................................................................................................................................
(2)
Sir George Monoux Sixth Form College
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(e)
(i)
In this investigation, the efficiency with which the energy in sunlight was converted
into energy in the biomass of the producers was found to be 4%. For every 10 000 kJ
of light energy falling on the beans, 400 kJ was therefore converted into energy in
producer biomass. Use the data in the graph to complete the diagram below which
shows the amount of biomass in the primary consumers and the secondary
consumers.
Energy in sunlight
10 000 kJ
4%
Energy in producer biomass
400 kJ
......... %
Energy in primary consumer biomass.
...... kJ
......... %
Energy in secondary consumer biomass.
...... kJ
(2)
(ii)
Explain why not all of the energy in producer biomass can be converted into energy
in primary consumer biomass.
...........................................................................................................................
...........................................................................................................................
...........................................................................................................................
(2)
(Total 14 marks)
2.
Hares are small mammals similar to rabbits. The diagram shows how some of the hares found in
southern Africa are classified.
Sir George Monoux Sixth Form College
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Animalia
Chordata
Mammalia
Lagomorpha
Leporidae
Lepus
Pronolagus
Pronolagus
randensis
Jameson's hare
Pronolagus
rupestris
Smith's hare
Sir George Monoux Sixth Form College
Pronolagus
crassicaudatus
Natal rock hare
Lepus
capensis
Cape hare
Lepus
saxatilis
Scrub hare
5
(a)
(i)
Name the genus to which the scrub hare belongs.
...........................................................................................................................
(1)
(ii)
Name the order to which the Natal rock hare belongs.
...........................................................................................................................
(1)
(b)
The map shows the distribution of three of these species of hare.
Key
Jameson's hare
Smith's hare
Natal rock hare
(i)
What is the evidence from the map that suggests that Smith’s hare and the Natal rock
hare are different species?
...........................................................................................................................
...........................................................................................................................
(1)
(ii)
Suggest what has caused the gene pools of the two populations of Jameson’s hare to
differ.
...........................................................................................................................
...........................................................................................................................
...........................................................................................................................
...........................................................................................................................
(2)
(Total 5 marks)
Sir George Monoux Sixth Form College
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3.
In cats, one of the genes for coat colour is present only on the X chromosome. This gene has two
alleles. The allele for ginger fur, XB, is dominant to that for black fur, Xb
(a)
All the cells in the body of a female mammal carry two X chromosomes. During an early
stage of development one of these becomes inactive and is not expressed. Therefore female
mammals have patches of cells with one X chromosome expressed and patches of cells with
the other X chromosome expressed. Tortoiseshell cats have coats with patches of ginger
and patches of black fur.
(i)
What is the genotype of a tortoiseshell cat?
...........................................................................................................................
(1)
(ii)
Explain why there are no male tortoiseshell cats.
...........................................................................................................................
(1)
(b)
A cat breeder who wished to produce tortoiseshell cats crossed a black female cat with a
ginger male. Complete the genetic diagram and predict the percentage of tortoiseshell
kittens expected from this cross.
Parental phenotypes:
black female
ginger male
Parental genotypes:
.........................
........................
Gamete genotypes:
.........................
........................
Offspring genotypes: ..................................................................................................
Percentage of tortoiseshell kittens: .............................................................................
(3)
(Total 5 marks)
Sir George Monoux Sixth Form College
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4.
The inheritance of the ABO blood groups is an example of multiple allele inheritance and is
controlled by three alleles of a single gene, IO, IA and IB
These three alleles determine the activity of an enzyme which modifies the structure of an antigen
on the cell surface membrane of the red blood cells. This is summarised below.
Antigen on cell surface
membrane
(a)
I O produces
inactive enzyme
Antigen
unchanged
I A produces enzyme
which adds acetylgalactosamine
to antigen
Antigen A
I B produces enzyme
which adds galactose
to antigen
Antigen B
In terms of mutation, explain each of the following statements.
(i)
The alleles IA and IB differ at several nucleotide positions but produce enzymes
which are very similar in their structure.
(2)
(ii)
The IO allele has a single base deletion and gives rise to an inactive enzyme.
(3)
(b)
Briefly explain how a DNA (gene) probe could be used to identify the presence of the 1o
allele in a sample of DNA,
(3)
(c)
The allele IO is recessive to both alleles IA and IB. Alleles IA and IB are codominant, that is,
they are both expressed in the phenotype.
The diagram shows the inheritance of ABO blood groups in one family.
1
2
A
3
5
4
B
O
AB
Female
6
7
Male
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(i)
Give the blood group genotype or genotypes of the sperm cells produced by
individual 2.
(1)
(ii)
Give the blood group phenotype of individual 1.
(1)
(iii)
Calculate the probability that the next child produced by individuals 4 and 5 will be a
boy with blood group A. Show your working.
(2)
(d)
Explain why a person with blood group O:
(i)
can safely give blood to someone with blood of any ABO type;
(2)
(ii)
can only safely receive blood from someone with blood group O
(2)
(e)
(i)
In a study of people living in India, the frequency of the IO allele was found to be
0.55 and that of the IA allele, 0.18. What was the frequency of the IB allele in this
population?
(1)
(ii)
Smallpox was an extremely severe disease which was particularly common among
the people of the Indian sub-continent. It has been suggested that the smallpox virus
had proteins on its surface which were very similar to the A antigen. Use this
information to suggest why people with blood groups B and O were less likely to
develop smallpox than those with blood groups A and AB.
(3)
(Total 20 marks)
5.
In an experiment, males and females of different species of fruit fly, Drosophila, were kept
together. Male fruit flies show complex courtship behaviour before they attempt to mate. The table
shows the percentage of females that mated when kept with males of different species.
Females
Males
Percentage of females that mated
D. serrata
D. serrata
90.2
D. serrata
D. birchii
0.7
D. serrata
D. dominicana
1.3
D. birchii
D. birchii
76.9
D. birchii
D. serrata
1.0
D. birchii
D. dominicana
0.4
D. dominicana
D. dominicana
93.0
D. dominicana
D. serrata
0.0
D. dominicana
D. birchii
3.7
Sir George Monoux Sixth Form College
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Sir George Monoux Sixth Form College
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(a)
In the classification of fruit flies, which biological subdivision is represented by the name
Drosophila?
.....................................................................................................................................
(1)
(b)
(i)
What do the data show about the mating preference of female Drosophila?
...........................................................................................................................
...........................................................................................................................
(1)
(ii)
Suggest an explanation for this mating preference.
...........................................................................................................................
...........................................................................................................................
...........................................................................................................................
...........................................................................................................................
(2)
(iii)
Suggest how these three species of Drosophila might have evolved from a common
ancestor.
...........................................................................................................................
...........................................................................................................................
...........................................................................................................................
...........................................................................................................................
(3)
(Total 7 marks)
6.
(a)
Explain the meaning of the term gene pool.
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
(1)
In two-spot ladybirds, the colour of the wing-cases is genetically determined. The allele for red
wing-cases, R, is dominant to that for black wing-cases, r.
(b)
In a ladybird with black wing-cases, how many copies of the r allele would you expect to
find in a nucleus taken from a muscle cell in the insect’s leg? Explain your answer.
.....................................................................................................................................
.....................................................................................................................................
(1)
Sir George Monoux Sixth Form College
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(c)
In a population of two-spot ladybirds found on a patch of nettles, 168 had red wing-cases
and 32 had black wing-cases. Showing your working in each case, calculate the frequency
of:
(i)
the r allele;
Answer: ............................................
(2)
(ii)
the R allele.
Answer: ............................................
(1)
(Total 5 marks)
7.
Answers should be written in continuous prose. Credit will be given for biological accuracy, the
organisation and presentation of the information and the way in which the answer is expressed.
Read the following passage
Bt is a toxin made by the soil bacterium, Bacillus thuringiensis. It is very toxic to insects so it is an
effective insecticide. Unfortunately, resistant strains have developed in the diamond-back moth,
whose caterpillars are important pests of crops of the cabbage family.
To try to overcome some of the problems of resistance, a programme of crop management was
developed. Studies showed that the allele which confers resistance on diamond-back moths was
recessive. Farmers were encouraged to leave a few untreated fields in which moths that were
susceptible to Bt would survive. If the rest of the fields were then sprayed with Bt, a few resistant
individuals would remain. However, because they were likely to mate with susceptible individuals
from the untreated fields, the number of resistant moths in the population would not increase.
(a)
Many populations of insect pest have become resistant to insecticides. Explain how
selection can result in an insect population which is resistant to a particular insecticide.
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
(5)
Sir George Monoux Sixth Form College
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(b)
(i)
Explain how the programme of crop management described in the second paragraph
prevents the number of resistant moths from increasing.
...........................................................................................................................
...........................................................................................................................
...........................................................................................................................
...........................................................................................................................
...........................................................................................................................
(ii)
Explain why this programme would not work if the resistance allele were dominant.
...........................................................................................................................
...........................................................................................................................
...........................................................................................................................
...........................................................................................................................
...........................................................................................................................
...........................................................................................................................
(6)
(Total 11 marks)
8.
In the flour beetle, the allele for red body colour (R) is dominant to the allele for black body colour
(r). A mixed culture of red beetles and black beetles was kept in a container in the laboratory under
optimal breeding conditions. After one year, there were 149 red beetles and 84 black beetles in the
container.
(a)
Use the Hardy-Weinberg equation to calculate the expected percentage of heterozygous red
beetles in this population.
Answer: ..............................................
(3)
Sir George Monoux Sixth Form College
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(b)
Several assumptions are made when using the Hardy-Weinberg equation. Give two of
these.
1..................................................................................................................................
2..................................................................................................................................
(2)
(Total 5 marks)
9.
(a)
The diagram shows an outline of the nitrogen cycle.
Nitrogen gas
in
atmosphere
Plant
protein
Animal
protein
Death and decay
in
soil
Ammonia
Nitrogen
gas
Process X
Substance A
Process Z
Name:
(i)
substance A;
...........................................................................................................................
(ii)
process X;
...........................................................................................................................
(iii)
process Z.
...........................................................................................................................
(3)
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(b)
The table shows the yield of a crop when different levels of nitrogen fertiliser were applied.
(i)
Nitrogen fertiliser
applied/ kg hectare–1
Yield/
tonnes hectare–1
0
2.8
50
3.3
100
4.2
150
4.7
200
4.7
Describe the effect that the fertiliser had on the yield of the crop.
...........................................................................................................................
...........................................................................................................................
(1)
(ii)
Explain two disadvantages of applying nitrogen fertiliser at levels above 150 kg
hectare–1.
1.........................................................................................................................
...........................................................................................................................
2.........................................................................................................................
...........................................................................................................................
(4)
(c)
The graphs show the range of heights of samples of two varieties of wheat grown under the
same conditions. Variety A is a modem form and Variety B is a form that was commonly
grown 100 years ago.
200
Number
of
plants
200
150
Number
of
plants
100
50
150
100
50
0
0
50
100
Height / cm
Variety A
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150
50
100
Height / cm
150
Variety B
15
(i)
Name the type of variation shown in these two graphs.
...........................................................................................................................
(1)
(ii)
Describe two differences shown in the graphs between Variety A and B.
1.........................................................................................................................
...........................................................................................................................
2.........................................................................................................................
...........................................................................................................................
(2)
(iii)
Suggest how the differences between the two varieties could have been brought
about.
...........................................................................................................................
...........................................................................................................................
...........................................................................................................................
...........................................................................................................................
(2)
(iv)
Suggest the advantages that these differences could have for modern farmers.
...........................................................................................................................
...........................................................................................................................
...........................................................................................................................
...........................................................................................................................
(2)
Assume that two genes affect the height of wheat plants and both of these genes have two
alleles. The table gives a summary of some possible genotypes and phenotypes.
Genotype
Phenotype
height of wheat/cm
AABB
100
AaBb
70
AAbb
70
aabb
40
Sir George Monoux Sixth Form College
16
A wheat plant that was 100 cm tall was crossed with a wheat plant that was 40 cm tall,
fertilisation occurred and the seeds were planted and grown.
(d)
Using only the information in the table, answer the following questions.
(i)
What are the genotypes of the gametes in this cross?
...........................................................................................................................
(1)
(ii)
What would be the expected genotype and phenotype of the resulting offspring?
Genotype ...........................................................................................................
Phenotype ..........................................................................................................
(2)
(Total 18 marks)
10.
The diagram shows three generations of a family.
1
2
5
6
3
4
7
8
9
10
11
Key:
Unaffected male
Unaffected female
Affected male
Affected female
No member of the family showed the symptoms of cystic fibrosis (CF) until the son was born in
the third generation. A single gene is responsible for the inheritance of cystic fibrosis.
(a)
Assume that no gene mutations have occurred in these generations. Use F for the dominant
allele and f for the recessive allele to give the possible genotype or genotypes of:
individual 7;.................................................................................................................
individual 11................................................................................................................
(2)
Sir George Monoux Sixth Form College
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(b)
Give the probability that the next child of parents 7 and 8 will be a girl with cystic fibrosis.
Show how you arrived at your answer.
Probability that child will be a girl with cystic fibrosis: ............................................
(2)
(c)
Attempts to treat cystic fibrosis using gene therapy have used viruses as vectors.
The viruses are introduced into the lungs using aerosols.
(i)
Explain why viruses are useful as vectors.
..........................................................................................................................
..........................................................................................................................
(1)
(ii)
Suggest a reason why gene therapy for the treatment of cystic fibrosis has not yet
been very successful.
..........................................................................................................................
..........................................................................................................................
(1)
(d)
In the UK, 1 in every 2 500 children has cystic fibrosis. What is the frequency of the cystic
fibrosis allele in children in the UK? Show how you arrived at your answer.
Frequency of cystic fibrosis allele: ...........................
(2)
(Total 8 marks)
Sir George Monoux Sixth Form College
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11.
In cats, some aspects of the inheritance of fur colour are sex linked. When a ginger male cat was
crossed with a black female, all the female kittens were tortoiseshell (a pattern of black hairs and
ginger hairs) and all the male kittens were black. However, in the reciprocal cross, although all the
female kittens were again tortoiseshell, the male kittens were ginger.
(a)
Complete the following genetic diagrams to explain the results of these two crosses.
Use the following symbols:
XB = an X-chromosome carrying an allele for black hair.
XG = an X-chromosome carrying an allele for ginger hair.
Cross 1
Cross 2
Parental phenotypes
Ginger x Black
male
female
Black
male
x Ginger
female
Parental genotypes
..........
..........
..........
..........
Gametes
................... ...................
................... ...................
Offspring genotypes
........................................
........................................
Offspring phenotypes
.......................................
.......................................
.......................................
.......................................
(4)
(b)
Why were no male tortoiseshell cats produced in these crosses?
.....................................................................................................................................
.....................................................................................................................................
(1)
(Total 5 marks)
Sir George Monoux Sixth Form College
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12.
Read the following passage.
In the living world, success may be measured by reproductive capacity. But this brings its own
problems: the more individuals there are, the greater the competition and struggle for survival.
5
10
15
In the early 1830s, Charles Darwin visited the Galapagos Islands, some 1000 km off the coast
of Ecuador, where he discovered several different species of small birds, called ground
finches. They all seemed to be related to similar birds found on the South American mainland
and Darwin suggested that they might therefore have originated from a common ancestor and
changed over the years to their present form. More recently, measurements have shown that
there are variations, not only between, but also within each species. For instance, on one of
the larger islands, called Albemarle, two species of ground finch share the same habitat. The
beaks of one species, Geospiza fortis, range in depth from 11 to 16 mm, while the other,
Geospiza fuliginosa, possesses beaks varying from 7 to 10 mm. On another island,
G. fuliginosa is absent and here G. fortis has a range of beak depths from 9 to 12mm.
What causes this divergence when living together? Perhaps competition is the answer. The
two species specialised by feeding on different-sized seeds. As beak depths diverged,
competition was reduced.
Use information from the passage and your own knowledge to answer the following question.
Explain how the process of natural selection on the two islands might have led to the different
ranges of beak depth in G. fortis.
...............................................................................................................................................
...............................................................................................................................................
...............................................................................................................................................
...............................................................................................................................................
...............................................................................................................................................
...............................................................................................................................................
...............................................................................................................................................
...............................................................................................................................................
(Total 7 marks)
13.
In tomato plants, the genes for flower colour and for height are on different chromosomes. The
allele for yellow flowers (Y) is dominant to that for white flowers (y) and the allele for tall plants
(T) is dominant to that for dwarf plants (t).
A tall tomato plant with yellow flowers was pollinated with pollen from a dwarf plant with white
flowers. The resulting seeds were planted and grew into plants with the following phenotypes:
Tall, yellow:
63
Dwarf, yellow: 58
Sir George Monoux Sixth Form College
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(a)
(i)
To what Mendelian ratio do these results approximate?
..........................................................................................................................
(1)
(ii)
Explain why the results of crosses like this only approximate to the expected
Mendelian ratio.
..........................................................................................................................
..........................................................................................................................
(1)
(b)
Use a genetic diagram to explain the results of this cross.
(3)
(Total 5 marks)
14.
Huntington’s disease is a human inherited condition resulting in gradual degeneration of nerve
cells in the brain. It is caused by a dominant allele but usually no symptoms are evident until the
person is at least 30 years old. It is very rare in most populations. However, in one isolated area in
Venezuela, 48% of the population possess a genotype which gives rise to Huntington’s disease.
Many of the inhabitants of this area can trace their origins back to a common ancestor 200 years
ago.
(a)
Use the Hardy-Weinberg equation to estimate the percentage of this Venezuelan population
which is heterozygous for Huntington’s disease. Show your working.
Answer = ....................................... %
(3)
Sir George Monoux Sixth Form College
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(b)
Suggest why
(i)
there is such a high incidence of Huntington’s disease in this population;
..........................................................................................................................
..........................................................................................................................
..........................................................................................................................
(ii)
Huntington’s disease has not been eliminated from this population by natural
selection.
..........................................................................................................................
..........................................................................................................................
..........................................................................................................................
(3)
(Total 6 marks)
15.
New Zealand beech trees do not produce seeds every year. A study was carried out on the mice
living in an isolated New Zealand beech forest. Because of the location of this forest, biologists
could only visit it at monthly intervals and stay approximately 12 hours on each visit.
At the beginning of each visit, they set all the traps they had available. This number varied. At the
end of the visit, they collected the traps and released any mice they had captured.
Figure 1 shows the population density of the mice at different times during a New Zealand beech
seed year and a non-seed year.
New Zealand beech
seed year
25
Number 20
of mice
captured 15
per 100
10
traps
Non-seed year
5
0
May
Aug
Nov
Month
Feb
May
Figure 1
Sir George Monoux Sixth Form College
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(a)
Use the information in the question to suggest
(i)
why the mark-release-recapture method would have given unreliable results;
..........................................................................................................................
..........................................................................................................................
..........................................................................................................................
..........................................................................................................................
(2)
(ii)
the advantage of giving the number of mice captured per 100 traps rather than just the
number of mice captured.
..........................................................................................................................
..........................................................................................................................
..........................................................................................................................
..........................................................................................................................
(2)
(b)
(i)
A statistical test was carried out on the August figures. The population density of
mice in the seed year was found to be significantly different at the p = 0.05 level from
the population density in the non-seed year. Explain the meaning of this statement.
..........................................................................................................................
..........................................................................................................................
..........................................................................................................................
..........................................................................................................................
(2)
(ii)
Suggest why the population density increases in a seed year.
..........................................................................................................................
..........................................................................................................................
..........................................................................................................................
..........................................................................................................................
(2)
Sir George Monoux Sixth Form College
23
In a different survey, mice were trapped at various sites in the UK. Figure 2 shows the mean body
mass and the standard deviation of the adult males that were among the trapped mice.
Refrigerated cold stores
Farms in Scotland
Farms in Wales
Farms in Northern England
12
14
16
18
20
Mass / g
22
24
26
Figure 2
(c)
(i)
Explain why the data for only the male mice were plotted in Figure 2.
..........................................................................................................................
..........................................................................................................................
(1)
(ii)
In collecting the raw data in this survey, the investigators also measured the amount
of tooth wear shown by the mice. Suggest why.
..........................................................................................................................
..........................................................................................................................
..........................................................................................................................
..........................................................................................................................
(2)
(d)
(i)
Explain the advantage of a large body mass to mice living in a refrigerated cold store.
..........................................................................................................................
..........................................................................................................................
..........................................................................................................................
..........................................................................................................................
(2)
Sir George Monoux Sixth Form College
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(ii)
Use the information in Figure 2 to explain what is meant by directional selection.
..........................................................................................................................
..........................................................................................................................
..........................................................................................................................
..........................................................................................................................
..........................................................................................................................
..........................................................................................................................
(3)
(e)
The colour of wild mice is grey but in some island populations there are black mice.
The difference in colour is caused by a single pair of alleles.
(i)
Describe how you could use genetic crosses to show that the allele for black is the
recessive allele.
..........................................................................................................................
..........................................................................................................................
..........................................................................................................................
..........................................................................................................................
(2)
(ii)
Explain how you could find the frequency of the recessive allele in a population of
mice living on an island.
..........................................................................................................................
..........................................................................................................................
..........................................................................................................................
..........................................................................................................................
(2)
(Total 20 marks)
16.
Read the following passage.
Despite its bad press, cholesterol is essential. We cannot manage without it. It is an important
component of plasma membranes. Myelin, the substance surrounding many nerve fibres, is
involved in the rapid conduction of nerve impulses and myelin is rich in cholesterol.
5
Being insoluble in water, cholesterol cannot be transported in solution in the blood plasma.
Instead, it is packaged in lipoprotein particles. The main carrier of cholesterol is low-density
lipoprotein (LDL). Each LDL particle has a cholesterol core protected by an outer coat and
topped by a special protein molecule.
Sir George Monoux Sixth Form College
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10
15
20
How is LDL-packaged cholesterol taken up by cells? Plasma membranes are studded with
binding sites for this "topping" protein. These LDL receptors are made of protein with some
sugar chains attached, and their numbers increase or decrease according to the cell's needs for
cholesterol. After latching on to LDL receptors, LDL particles are pulled into the cytoplasm
and processed in various ways. This regulatory mechanism, however, cannot control
cholesterol concentrations outside cells when large amounts of cholesterol are present in the
blood. The excess cholesterol is eventually deposited in artery walls. This leads to an increased
risk of thrombosis.
In the 1980s, researchers purified the LDL receptor molecule and determined the sequence of
its 839 amino acids. They also isolated the LDL receptor gene. Mutation of this gene gives rise
to a condition known as familial hypercholesterolemia (FH). All the evidence we have, such
as that all affected individuals have at least one affected parent, and that male to male
transmission is possible, indicates that the mutant allele is dominant and located on one of the
autosomes.
The FH allele is found in a high frequency in some populations. Among South African
Afrikaners, for example, 1 in 100 are FH heterozygotes while 1 in 30 000 are homozygous for
the FH allele. These people are all at risk of premature death from coronary heart disease.
Source: adapted from MANGE and MANGE, Basic Human Genetics (Sinaeur Associates Inc.) 1994
Use information from the passage and your own knowledge to answer the following questions.
(a)
Explain how myelin is involved in the rapid conduction of nerve impulses (lines 2-3).
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
(2)
(b)
Describe how negative feedback is involved in controlling the concentration of cholesterol
in the cytoplasm of a cell.
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
(3)
(c)
(i)
Explain how a mutation of the LDL receptor gene can lead to a high concentration of
cholesterol in the blood.
..........................................................................................................................
..........................................................................................................................
..........................................................................................................................
..........................................................................................................................
(2)
Sir George Monoux Sixth Form College
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(ii)
Describe how excess cholesterol deposited in artery walls can lead to an increased
risk of thrombosis (lines 14-15).
..........................................................................................................................
..........................................................................................................................
..........................................................................................................................
..........................................................................................................................
(2)
(d)
What is the minimum number of nucleotides in the mRNA molecule that codes for the LDL
receptor? Explain how you arrived at your answer.
.....................................................................................................................................
.....................................................................................................................................
(1)
(e)
All individuals affected with FH have at least one affected parent (line 19).
Explain how this shows that the FH allele is not recessive to the normal allele.
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
(2)
(f)
Use the data in the last paragraph to estimate the number of people in the South African
Afrikaner population at risk from premature death from coronary heart disease because of
FH. Give your answer per 100 000 of the population. Show your working.
Answer .................................... per 100 000
(3)
(Total 15 marks)
17.
In humans, cystic fibrosis is caused by a recessive allele, f.
(a)
What is an allele?
.....................................................................................................................................
.....................................................................................................................................
(1)
Sir George Monoux Sixth Form College
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(b)
A man and woman are both heterozygous for the cystic fibrosis allele. They have one
healthy son but would like to have another child. ‘What is the probability that they will
produce a girl who has cystic fibrosis? Show your working.
Probability = .........................................
(2)
(Total 3 marks)
18.
(a)
What is meant by reproductive isolation?
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
(1)
(b)
Explain how geographical isolation can lead to the formation of new species.
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
(4)
(Total 5 marks)
Sir George Monoux Sixth Form College
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19.
The inheritance of body colour in fruit flies was investigated. Two fruit flies with grey bodies were
crossed. Of the offspring, 152 had grey bodies and 48 had black bodies.
(a)
Using suitable symbols, give the genotypes of the parents. Explain your answer.
Genotypes ..................................................................................................................
Explanation ................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
(2)
(b)
(i)
Explain why a statistical test should be applied to the data obtained in this
investigation.
...........................................................................................................................
...........................................................................................................................
...........................................................................................................................
...........................................................................................................................
(2)
(ii)
The null hypothesis in this investigation predicted that there would be no difference
between the observed and expected values. Use the table to determine whether this
hypothesis can be supported. Explain how you arrived at your answer.
Degrees of
freedom
Probability value
0.99
9.95
0.1
0.05
0.01
0.001
1
0.0002
0.0039
2.71
3.84
6.63
10.83
2
0.020
0.103
4.61
5.99
9.21
13.82
3
0.115
0.352
6.25
7.81
11.34
16.27
4
0.297
0.711
7.78
9.49
13.28
18.47
...........................................................................................................................
...........................................................................................................................
...........................................................................................................................
...........................................................................................................................
(2)
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(c)
A species of insect, only found on a remote island, has a characteristic controlled by a pair
of codominant alleles, CM and CN.
(i)
What is meant by codominant?
...........................................................................................................................
...........................................................................................................................
(1)
(ii)
There were 500 insects in the total population. In this population, 300 insects had the
genotype CM CM, 150 had the genotype CM CN and 50 had the genotype
CN CN. Calculate the actual frequency of the allele CN by using these figures. Show
your working.
Answer ........................................
(2)
(iii)
Use your answer to (c) (ii) and the Hardy-Weinberg equation to calculate the number
of insects that would be expected to have the genotype CN CN.
Answer ........................................
(3)
(Total 12 marks)
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20.
(a)
Caterpillars were fed on diets in which different amino acids were absent. Figure 1 shows
the percentage of caterpillars which survived on these diets for 20 days.
100
80
Percentage of
60
caterpillars
surviving for
20 days
40
20
0
Control
group
Valine
Leucine
Proline
Glutamate
Amino acid absent from diet
Figure 1
(i)
Describe how the control group of caterpillars should have been treated.
...........................................................................................................................
...........................................................................................................................
...........................................................................................................................
...........................................................................................................................
(2)
(ii)
In caterpillars, glutamate is a non-essential amino acid. Explain the evidence from
Figure 1 which supports this.
...........................................................................................................................
...........................................................................................................................
...........................................................................................................................
...........................................................................................................................
(2)
Sir George Monoux Sixth Form College
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The rate of uptake of amino acids by the epithelial cells lining a piece of rat small intestine was
investigated. Two experiments were carried out. In experiment A, the contents of the intestine
were stirred while the measurements were taken. In experiment B, the contents of the intestine
were not stirred. The table shows the results of these experiments.
(b)
Concentration of amino
acids in intestine/
mmol dm –3
A. Contents stirred
0
0
0
2
5.1
2.9
4
7.8
5.6
6
9.4
6.5
8
10.8
7.2
10
11.1
7.5
(i)
Rate of uptake of amino acids / arbitrary units
B. Contents not stirred
In experiment B, describe how the rate of uptake changes as the concentration of
amino acids in the intestine increases.
...........................................................................................................................
...........................................................................................................................
...........................................................................................................................
...........................................................................................................................
(2)
(ii)
It has been suggested that carrier proteins are involved in transporting amino acids
from the intestine. Explain how the results of experiment B support this suggestion.
...........................................................................................................................
...........................................................................................................................
...........................................................................................................................
...........................................................................................................................
(2)
(c)
(i)
Explain how mixing the intestine contents increases the rate of absorption of amino
acids.
...........................................................................................................................
...........................................................................................................................
...........................................................................................................................
...........................................................................................................................
(2)
(ii)
Which tissue, present in the wall of the intestine, mixes the contents of the intestine in
a live animal?
Sir George Monoux Sixth Form College
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...........................................................................................................................
(1)
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Figure 2 shows some biochemical pathways involving the amino acid phenylalanine in the human
body.
From protein
in diet
Phenylalanine
hydroxylase
Phenylalanine
H
H
N
H
C
Tyrosine
O
H
OH
H
C
H
N
CH 2
C
O
C
OH
CH 2
OH
Phenyl pyruvic acid
and other substances
Thyroid hormone
DOPA
Melanin
Dopamine
(Brain neurotransmitter)
Causes damage to
growing brain
Noradrenaline and adrenaline
Figure 2
(d)
Explain why the enzyme which converts phenylalanine into tyrosine is called phenylalanine
hydroxylase.
.....................................................................................................................................
.....................................................................................................................................
(1)
(e)
Phenylketonuria is a genetic disease in which the enzyme phenylalanine hydroxylase
(PAH) is missing. If untreated, phenylketonuria causes damage to the growing brain.
Suggest and explain one other sign or symptom of phenylketonuria.
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
(3)
Sir George Monoux Sixth Form College
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(f)
Babies who are diagnosed as having phenylketonuria are fed on a special diet that contains
only small amounts of phenylalanine and extra tyrosine. This special diet is necessary only
until the child reaches the age of about 6 years. After this a normal but low-protein diet is
recommended.
(i)
Explain why the special diet contains extra tyrosine.
...........................................................................................................................
...........................................................................................................................
...........................................................................................................................
...........................................................................................................................
(2)
(ii)
Explain why the special diet is only necessary until the child reaches the age of about
6 years.
...........................................................................................................................
...........................................................................................................................
(1)
(g)
A woman who has phenylketonuria may have a child who does not have this condition. It is
important that a woman with phenylketonuria keeps to the special diet throughout her
pregnancy, otherwise her child will be born with brain damage. Explain why.
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
(2)
(Total 20 marks)
21.
In the squirting cucumber, there are three kinds of plants; plants with male flowers only, plants
with female flowers only, and hermaphrodite plants with both male and female flowers. Sex is
determined by a single gene with three alleles.
AD is the allele for male. It is dominant over the other two alleles.
A+ is the allele for hermaphrodite. It is dominant over allele Ad.
Ad is the allele for female. It is recessive to the other two alleles.
(a)
(i)
Give the genotype of a female squirting cucumber.
..............................................................................................................................
(1)
Sir George Monoux Sixth Form College
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(ii)
Explain why a male squirting cucumber cannot have the genotype ADAD.
..............................................................................................................................
..............................................................................................................................
..............................................................................................................................
..............................................................................................................................
(2)
(b)
Complete the genetic diagram to show how it would be possible for a cross between two
hermaphrodite plants to produce female offspring.
Parent phenotypes:
Parent genotypes:
hermaphrodite
×
hermaphrodite
Gametes:
Offspring genotypes:
(2)
(Total 5 marks)
22.
(a)
Explain what is meant by a gene pool.
...........................................................................................................................................
...........................................................................................................................................
...........................................................................................................................................
...........................................................................................................................................
(2)
Sir George Monoux Sixth Form College
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(b)
Greater willow herb is a common plant found in damp places. It usually has red flowers
controlled by the allele R. Plants with the genotype rr, however, have white flowers.
In a sample of plants growing beside a ditch, 17 had white flowers and 327 had red flowers.
(i)
Calculate the frequency of the r allele in this sample. Show your working.
Frequency of r allele = .......................................................
(2)
(ii)
The Hardy-Weinberg equation could be used to find the frequencies of the different
genotypes in the population from which this sample was taken. Give one assumption
that must be made if the equation is to be applied.
..............................................................................................................................
..............................................................................................................................
(1)
(Total 5 marks)
23.
Cyanide is a poisonous substance. Cyanogenic clover plants produce cyanide when their tissues
are damaged. The ability to produce cyanide is controlled by genes at loci on two different
chromosomes. The dominant allele, A, of one gene controls the production of an enzyme which
converts a precursor to linamarin. The dominant allele, L, of the second gene controls the
production of an enzyme which converts linamarin to cyanide. This is summarised in the diagram.
Allele A
Allele L
Enzyme A
Enzyme L
Precursor
(a)
Linamarin
Cyanide
Acyanogenic clover plants cannot produce cyanide. Explain why a plant with the genotype
aaLl cannot produce cyanide.
...........................................................................................................................................
...........................................................................................................................................
(1)
(b)
A clover plant has the genotype AaLl.
(i)
Give the genotypes of the male gametes which this plant can produce.
..............................................................................................................................
(1)
Sir George Monoux Sixth Form College
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(ii)
Explain how meiosis results in this plant producing gametes with these genotypes.
..............................................................................................................................
..............................................................................................................................
..............................................................................................................................
..............................................................................................................................
(2)
(c)
Two plants, heterozygous for both of these pairs of alleles, were crossed. What proportion
of the plants produced from this cross would you expect to be acyanogenic but able to
produce linamarin? Use a genetic diagram to explain your answer.
(3)
In an investigation, cyanogenic and acyanogenic plants were grown together in pots. Slugs were
placed in each pot and records were kept of the number of leaves damaged by the feeding of the
slugs over a period of 7 days. The results are shown in the table.
(d)
Undamaged
Damaged
Cyanogenic
160
120
Acyanogenic
88
192
A 2 test was carried out on the results.
(i)
Suggest the null hypothesis that was tested.
..............................................................................................................................
..............................................................................................................................
(1)
Sir George Monoux Sixth Form College
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(ii)
2 was calculated. When this value was looked up in a table, it was found to
correspond to a probability of less than 0.05. What conclusion can you draw from
this?
..............................................................................................................................
..............................................................................................................................
..............................................................................................................................
..............................................................................................................................
..............................................................................................................................
..............................................................................................................................
(3)
A second investigation was carried out in a field of grass which had been undisturbed for many
years. The table shows the population density of slugs and the numbers of cyanogenic and
acyanogenic clover plants at various places in the field.
Population density of slugs
Number of acyanogenic
clover plants per m2
Number of cyanogenic
clover plants per m2
Very low
26
10
Low
17
26
High
0
10
Very High
0
5
(e)
Explain the proportions of the two types of clover plant in different parts of the field.
...........................................................................................................................................
...........................................................................................................................................
...........................................................................................................................................
...........................................................................................................................................
...........................................................................................................................................
...........................................................................................................................................
...........................................................................................................................................
...........................................................................................................................................
(4)
(Total 15 marks)
Sir George Monoux Sixth Form College
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24.
Duchenne muscular dystrophy is a sex-linked inherited condition which causes degeneration of
muscle tissue. It is caused by a recessive allele. The diagram shows the inheritance of muscular
dystrophy in one family.
1
3
4
10
11
5
2
6
7
8
12
9
13
14
15
Key:
= male with muscular dystrophy
= unaffected male
= female with muscular dystrophy
= unaffected female
(a)
Give evidence from the diagram which suggests that muscular dystrophy is
(i)
sex-linked; ..................................................................................................................
.....................................................................................................................................
(1)
(ii)
caused by a recessive allele. .......................................................................................
.....................................................................................................................................
(1)
Sir George Monoux Sixth Form College
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(b)
Using the following symbols,
XD = an X chromosome carrying the normal allele
Xd = an X chromosome carrying the allele for muscular dystrophy
Y = a Y chromosome
give all the possible genotypes of each of the following persons.
5 .....................................................................................................................................
6 .....................................................................................................................................
7 .....................................................................................................................................
8 .....................................................................................................................................
(2)
(c)
A blood test shows that person 14 is a carrier of muscular dystrophy. Person 15 has recently
married person 14 but as yet they have had no children. What is the probability that their
first child will be a male who develops muscular dystrophy?
.....................................................................................................................................
(1)
(Total 5 marks)
25.
Warfarin is a substance which inhibits blood clotting. Rats which eat warfarin are killed due to
internal bleeding. Some rats are resistant to warfarin as they have the allele WR.
Rats have three possible genotypes:
WRWR resistant to warfarin
WRWS resistant to warfarin
WSWS susceptible (not resistant) to warfarin.
In addition, rats with the genotype WRWR require very large amounts of vitamin K in their diets.
If they do not receive this they will die within a few days due to internal bleeding.
(a)
How can resistance suddenly appear in an isolated population of rats which has never
before been exposed to warfarin?
..............................................................................................................….....................
..............................................................................................................….....................
(1)
Sir George Monoux Sixth Form College
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(b)
A population of 240 rats was reared in a laboratory. They were all fed on a diet containing
an adequate amount of vitamin K. In this population, 8 rats had the genotype WSWS, 176
had the genotype WRWS and 56 had the genotype WRWR.
(i)
Use these figures to calculate the actual frequency of the allele WR in this population.
Show your working.
Answer ..................................
(2)
(ii)
The diet of the rats was then changed to include only a small amount of vitamin K.
The rats were also given warfarin. How many rats out of the population of 240 would
be likely to die within a few days?
............................................................................................................................
(1)
(c)
In a population of wild rats, 51% were resistant to warfarin.
(i)
Use the Hardy-Weinberg equation to estimate the percentage of rats in this
population which would be heterozygous for warfarin resistance. Show your
working.
Answer ....................................... %
(3)
(ii)
If all the susceptible rats in this population were killed by warfarin, more susceptible
rats would appear in the next generation. Use a genetic diagram to explain how.
Sir George Monoux Sixth Form College
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(2)
Sir George Monoux Sixth Form College
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(iii)
The graph shows the change in the frequency of the WS allele in an area in which
warfarin was regularly used. Describe and explain the shape of the curve.
Frequency
of W S allele
Time
......................................………..........................................................................
............................................................................................................................
............................................................................................................................
............................................................................................................................
............................................................................................................................
............................................................................................................................
............................................................................................................................
............................................................................................................................
(4)
(iv)
Give two assumptions that must be made when using the Hardy-Weinberg equation.
1 .........................................................................................................................
............................................................................................................................
2 .........................................................................................................................
............................................................................................................................
(2)
(Total 15 marks)
Sir George Monoux Sixth Form College
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26.
In fruit flies, the allele for grey body, G, is dominant to the allele for ebony body, g, and the allele
for normal wings, N, is dominant to the allele for vestigial wings, n. Vestigial-winged flies,
heterozygous for grey body colour, were crossed with ebony-bodied flies, heterozygous for
normal wings.
Complete the genetic diagram to show the genotypes and phenotypes in this cross.
Parental phenotypes
Grey body, vestigial wings
Ebony body, normal wings
Parental genotypes
..............................
...............................
Gamete genotypes
..............................
...............................
Offspring genotypes ............................................................................................................
Offspring phenotypes ..........................................................................................................
(Total 4 marks)
27.
(a)
Explain the meaning of these ecological terms.
Population .…..............................................................................................................
............………..............................................................................................................
Community ............………..........................................................................................
............………..............................................................................................................
(2)
Sir George Monoux Sixth Form College
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(b)
Some students used the mark-release-recapture technique to estimate the size of a
population of woodlice. They collected 77 woodlice and marked them before releasing
them back into the same area. Later they collected 96 woodlice, 11 of which were marked.
(i)
Give two conditions necessary for results from mark-release-recapture investigations
to be valid.
1 ........................................................................................................................
...........................................................................................................................
2 ........................................................................................................................
...........................................................................................................................
(2)
(ii)
Calculate the number of woodlice in the area under investigation. Show your
working.
Answer ......................................................
(2)
(c)
Explain how you would use a quadrat to estimate the number of dandelion plants in a field
measuring 100 m by 150 m.
............………..............................................................................................................
............………..............................................................................................................
............………..............................................................................................................
............………..............................................................................................................
............………..............................................................................................................
............………..............................................................................................................
(3)
Sir George Monoux Sixth Form College
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(d)
Two similar species of birds (species A and species B) feed on slightly different sized
insects and have slightly different temperature preferences. The diagram represents the
response of each species to these factors.
Tolerance of individuals
of each species
1
2
Species A
Temperature
5
Species B
3
4
Number of
prey items
eaten by
individuals
of each
species
Species A
Species B
Size of food item
(i)
Which of the numbered boxes describes conditions which represent
the niche of species A;
................
the niche of species B;
................
insects too small for species B and temperature too warm for species A; ................
insects too large for species A and temperature too cool for species B?
.................
(2)
Sir George Monoux Sixth Form College
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(ii)
These two species are thought to have evolved as a result of sympatric speciation.
Suggest how this might have occurred.
...........................................................................................................................
...........................................................................................................................
...........................................................................................................................
...........................................................................................................................
...........................................................................................................................
...........................................................................................................................
...........................................................................................................................
(4)
(Total 15 marks)
28.
(a)
Explain what is meant by stabilising selection and describe the circumstances under which
it takes place.
............………..............................................................................................................
............………..............................................................................................................
............………..............................................................................................................
............………..............................................................................................................
............………..............................................................................................................
............………..............................................................................................................
............………..............................................................................................................
............………..............................................................................................................
............………..............................................................................................................
(5)
Sir George Monoux Sixth Form College
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(b)
Some European clover plants can produce cyanide. Those plants that can produce cyanide
are called cyanogenic; those that cannot produce cyanide are called acyanogenic. Cyanide
is toxic to the cells of animals and plants.
When the leaves of cyanogenic plants are damaged by slugs, or exposed to low
temperatures, membranes within the cells are broken. This causes the release of the
enzymes that control the reactions which produce cyanide.
The proportions of cyanogenic and acyanogenic plants in clover populations were
determined in different parts of Europe. These are shown in the diagram below, together
with the mean minimum winter temperatures. Slugs are not usually active at temperatures
below 0 °C.
–4 °C
0 °C
4 °C
10 °C
Key
Cyanogenic
plants
Acyanogenic
plants
Population of
clover plants
Sir George Monoux Sixth Form College
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Explain the proportions of cyanogenic and acyanogenic plants in clover populations
growing in the area where the mean minimum winter temperature is below –4°C and in the
area where it is above 10 °C.
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
(5)
(Total 10 marks)
29.
Human ABO blood groups are determined by the presence or absence of two antigens (A and B)
on the plasma membrane of the red blood cells. The inheritance of these blood groups is controlled
by three alleles:
IA – determines the production of antigen A
IB – determines the production of antigen B
Io – determines the production of no antigen
Alleles I A and I B are codominant. Allele I o is recessive to both.
The pedigree shows the pattern of inheritance of these blood groups in a family over three
generations.
B
4
A
3
A
1
B
2
AB
5
A
6
B
7
A
AB
AB
B
O
9
10
11
12
13
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8
50
(a)
(i)
How many antigen-determining alleles will be present in a white blood cell? Give a
reason for your answer.
...........................................................................................................................
...........................................................................................................................
(1)
(ii)
Which antigen or antigens will be present on the plasma membranes of red blood
cells of individual 5?
...........................................................................................................................
(1)
(b)
If individuals 6 and 7 were to have another child, what is the probability that this child
would be male and blood group A? Explain your answer.
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
(3)
(Total 5 marks)
30.
(a)
Some antibiotics bind with specific receptors in the plasma membranes of bacteria.
The structure of these receptors is determined genetically. Bacteria can become resistant to
an antibiotic because a gene mutation results in an altered receptor.
Explain how resistance to an antibiotic could become widespread in a bacterial population
following a gene mutation conferring resistance in just one bacterium.
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
Sir George Monoux Sixth Form College
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(5)
Sir George Monoux Sixth Form College
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(b)
Some humans have a genetic resistance to infection. A recessive allele gives increased
resistance to infection by the malarial parasite. In a population, the proportion of babies
born who are homozygous for this allele is 0.01. Use the Hardy-Weinberg equation to
calculate the expected proportion of heterozygotes in this population. Show your working.
Answer ............................................
(4)
(Total 9 marks)
31.
Chickens have a structure on their heads called a comb. The diagram shows four types of comb:
walnut, pea, rose and single.
Two genes control the type of comb; each gene has a dominant and a recessive allele. The two
genes are inherited independently, but interact to produce the four types of comb.
Sir George Monoux Sixth Form College
Genotype
Phenotype
A- B-
Walnut
A- bb
Pea
aa B-
Rose
aa bb
Single
53
The symbol - indicates that either the dominant allele or recessive allele could be present
Sir George Monoux Sixth Form College
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(a)
A male with a pea comb, heterozygous for gene A, was crossed with a rose-combed female,
heterozygous for gene B. Complete the genetic diagram to show the offspring expected
from this cross.
Phenotypes of parents
Pea comb
Rose comb
Genotypes of parents
………………
………………
Gametes formed
………………
………………
Offspring genotypes
…………………………………………
Ratio of offspring phenotypes
…………………………………………
………………………………………….
(3)
(b)
Chickens with rose or single combs made up 36% of one population. Assuming the
conditions of the Hardy-Weinberg equilibrium apply, calculate the frequency of allele a in
this population. Show how you arrived at your answer.
Frequency of allele a = ......................................
(2)
(Total 5 marks)
Sir George Monoux Sixth Form College
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32.
There is evidence that the first photosynthetic organisms were primitive water-dwelling bacteria.
The very first of these lived near the surface of the water in lakes and contained a purple pigment
that absorbed light most strongly in the green region of the spectrum. Later, other bacteria evolved
that lived on the top of sediment at the bottom of the lakes (Figure 1). Gene mutations had enabled
these bacteria to synthesise chlorophyll instead of the purple pigment present in the bacteria living
near to the surface. Chlorophyll absorbs light most strongly in the blue and red regions of the
spectrum (Figure 2).
Figure 1
Light energy
First bacteria lived near
the surface of the water
Later bacteria
lived on top of
the sediment at the
bottom of the lake
Figure 2
Pigment from
surface-dwelling
bacteria
Chlorophyll
from sediment-dwelling
bacteria
Absorbtion
400
Blue
500
Green
600
Red
700
Wavelength of light
Sir George Monoux Sixth Form College
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(a)
Describe how light energy absorbed by chlorophyll molecules is used to synthesise ATP.
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
(5)
(b)
Use Figure 2 to explain how natural selection would favour the evolution of
sediment-dwelling bacteria containing a different photosynthetic pigment from those living
near the surface of the water.
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
(6)
(Total 11 marks)
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33.
Finches are small birds. Fourteen species of finch are found on the Galapagos Islands.
(a)
What is a species?
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
(2)
(b)
Measurements were made of the beak depth of two species of finch (species A and species
B) on different islands. Species A is found on island 1, species B is found on island 2. Both
species are found on island 3. They are thought to have colonised island 3 from islands 1
and 2 respectively. The graphs show the ranges of beak depths of the two species on the
different islands.
Species A on island 1
40
Percentage of
population
20
0
7
8
9
10
11
12
13
14
15
16
Beak depth / mm
Species B on island 21
40
Percentage of
population
20
0
7
8
9
10
11
12
13
14
15
16
Beak depth / mm
60
Species A and B on island 3
40
Percentage of
population
Species B
Species A
20
0
7
8
9
10
11
12
13
14
15
16
Beak depth / mm
Sir George Monoux Sixth Form College
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What type of natural selection took place in the populations of both species after they had
colonised island 3? Explain your answer.
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
(3)
(Total 5 marks)
34.S Red-green colour blindness is caused by a mutation in the gene coding for one of the opsin
proteins which are needed for colour vision. The diagram shows the inheritance of red-green
colour blindness in one family.
1
5
2
6
3
7
10
8
11
4
9
12
14
13
15
16
Key
= colour-blind male
= unaffected male
= unaffected female
Sir George Monoux Sixth Form College
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Person 12 is pregnant with her fourth child. What is the probability that this child will be a male
with red-green colour blindness? Explain your answer by drawing a genetic diagram. Use the
following symbols
XR = an X chromosome carrying an allele for normal colour vision
Xr= an X chromosome carrying an allele for red-green colour blindness
Y = a Y chromosome
Probability = ......................................
(Total 4 marks)
35.
The inheritance of ABO blood groups is controlled by three alleles of the same gene, IA IB and IO.
The alleles IA and IB are codominant. Both IA and IB are dominant to the allele IO.
(a)
Explain what is meant by an allele.
....................................................................................................................................
....................................................................................................................................
(1)
Sir George Monoux Sixth Form College
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(b)
(i)
Complete the table to show the missing genotypes.
Blood group
phenotype
Possible
genotype
A
IAIA,
..........
B
IBIB,
..........
AB
......................
O
......................
(2)
(ii)
Children of blood groups A and O were born to parents of blood groups A and B.
Complete the genetic diagram to show the possible ABO blood group phenotypes of
the children which could be produced from these parents.
Parental phenotypes
Blood group A
Blood group B
Parental genotypes
Genotypes of gametes
Genotypes of children
Phenotypes of children
(3)
(Total 6 mark)
Sir George Monoux Sixth Form College
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36.
The fruit fly is a useful animal for studying genetic crosses. The diagram shows the life cycle of
the fruit fly.
Male
Female
Mating occurs and female
lays fertilised eggs 24 hours
after emerging.
Adult (2 mm)
Sperm
Egg
Fertilised egg (0.5 mm)
Single female lays between
80 and 200 eggs.
Egg hatches into larva
about one day after laying
Larva (4.5 mm)
Larva moults twice and
changes into pupa about
6 days after laying.
Adult fly
emerges from
pupa about
10 days after
laying.
(a)
Pupa (3 mm)
Using information from the diagram explain three ways in which the fruit fly is a useful
animal for studying genetic crosses.
1. ................................................................................................................................
....................................................................................................................................
2. ................................................................................................................................
....................................................................................................................................
3. ................................................................................................................................
....................................................................................................................................
(3)
Sir George Monoux Sixth Form College
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In fruit flies the allele for grey body colour, G, is dominant to the allele for black body, g, and the
allele for normal wings, N, is dominant to the allele for vestigial wings, n. A cross between a
grey-bodied, normal-winged fly and a black-bodied, vestigial-winged fly resulted in the following
offspring.
25 grey-bodied, normal-winged
26 grey-bodied, vestigial-winged
24 black-bodied, normal-winged
27 black-bodied, vestigial-winged
(b)
(i)
Give the genotype of the grey-bodied, normal-winged parent.
...........................................................................................................................
(1)
(ii)
Give the genotypes of the gametes which could be produced by one of the
grey-bodied, vestigial-winged offspring.
...........................................................................................................................
(1)
(c)
What ratio would you expect in the offspring produced if the grey-bodied, normal-winged
parent had been crossed with a fly of the same genotype?
....................................................................................................................................
(1)
(Total 6 marks)
37.
Read the following passage.
Madagascar
The island of Madagascar has been described as the laboratory of evolution. It broke away from
mainland Africa at least 120 million years ago and, following this, many new species developed.
Estimates of the number of plant species on the island vary from 7 370 to 12 000, making it
botanically one of the richest areas in the world. Of 400 flowering plant families found worldwide,
200 grow only in Madagascar. Among animals, true lemurs are found nowhere else, and 95 per
cent of the country’s 235 known species of reptiles evolved on the island. Over the past 25 years
the human population has doubled. Land shortage is leading to clearing of the forest, and
Madagascar is now facing deforestation on a massive scale. Scientists have estimated that even if
the forest could recover, regeneration could take up to a hundred years.
(Reproduced with permission from New Scientist magazine  RBI Ltd)
(a)
Explain what is meant by the term species.
....................................................................................................................................
....................................................................................................................................
(2)
Sir George Monoux Sixth Form College
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(b)
(i)
Explain the processes which might have led to the evolution of new species on the
island.
...........................................................................................................................
...........................................................................................................................
...........................................................................................................................
...........................................................................................................................
...........................................................................................................................
...........................................................................................................................
...........................................................................................................................
...........................................................................................................................
(4)
(ii)
Suggest and explain how the number of animal species on the island may have
changed as it became ‘botanically one of the richest areas in the world’.
...........................................................................................................................
...........................................................................................................................
...........................................................................................................................
...........................................................................................................................
(2)
(c)
Describe the processes by which forest is able to regenerate after being cleared.
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
(4)
(Total 12 marks)
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38.
The diagram shows the pathway by which phenylalanine is normally metabolised.
phenylalanine
enzyme A
tyrosine
DOPA
melanin
(dark pigment in skin, hair and eyes)
dopamine
(brain transmitter involved in motor coordination)
Phenylketonuria (PKU) is a condition which results from the absence of enzyme A.
People with PKU are homozygous for a recessive allele which fails to produce this enzyme.
(a)
Use the information shown in the diagram to give one symptom you might expect to be
visible in a person who inherits PKU.
.....................................................................................................................................
(1)
(b)
Explain how gene mutation may result in an allele which fails to produce a functional
enzyme.
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
(3)
Sir George Monoux Sixth Form College
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(c)
(i)
A child with PKU was born to two unaffected parents. Complete the genetic diagram
to show how this is possible.
Parental phenotypes
Parental genotypes
Genotypes of gametes
Genotypes of children
Phenotypes of children
(2)
(ii)
What is the probability that a second child born to these parents will have PKU?
...........................................................................................................................
(1)
(Total 7 marks)
39.
Tongue-rolling and red-green colour blindness are two genetically controlled conditions which
occur in humans. Tongue-rolling is controlled by the dominant allele, T, while non-rolling is
controlled by the recessive allele, t.
Red-green colour blindness is controlled by a sex-linked gene on the X chromosome. Normal
colour vision is controlled by the dominant allele, B, while red-green colour blindness is
controlled by the recessive allele, b.
Sir George Monoux Sixth Form College
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(a)
Complete the genetic diagram to show the possible genotypes and phenotypes which could
be produced from the following parents.
Female
Colour blind and heterozygous
for tongue-rolling.
Male
Normal colour vision
and non-roller
Parental genotypes
Genotypes of gametes
Genotypes of children
Sex and phenotypes of children
(4)
(b)
Explain why a higher percentage of males than females in a population is red-green colour
blind.
.....................................................................................................................................
.....................................................................................................................................
(c)
Sex-linked genes on the Y chromosome have been found in humans and other animal
species. Suggest and explain one piece of evidence which would support the presence of
such a gene.
.....................................................................................................................................
.....................................................................................................................................
(1)
(Total 6 marks)
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40.
Fourteen different species of finch live on the isolated Galapagos Islands. The finches are believed
to have all evolved from a single common ancestor. The diagram shows the suggested
evolutionary relationships amongst the species.
Carmahynchus
Certhidia
olivacea
Pinaroloxia
inornata
heliobates
pallidus
WARBLER
Geospiza
pauper
parvulus
fuliginosa
crassirostris
magnirostris
scandens
psittacula
conirostris
WOODPECKER
difficilis
fortis
FINCHES
INSECT EATERS
SEED EATERS
SEED-EATING
GROUND FINCH
ANCESTOR
(a)
Suggest why these fourteen types of finch are considered to be different species.
.....................................................................................................................................
.....................................................................................................................................
(1)
(b)
Use the information in the diagram to identify
(i)
the species of ground finch which eats the largest seeds;
...........................................................................................................................
(ii)
the number of genera which are present on the islands.
...........................................................................................................................
(2)
(c)
Suggest how two distinct species, one insect-eating and the other seed-eating, may have
evolved from a common ancestor.
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
(4)
(Total 7 marks)
Sir George Monoux Sixth Form College
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Sir George Monoux Sixth Form College
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41.
Some forms of clover are cyanogenic. They produce poisonous hydrogen cyanide when their
tissues are damaged. The production of hydrogen cyanide takes place in two steps, each of which
is catalysed by an enzyme produced by a different gene.
Dominant
allele A
Dominant
allele B
Enzyme A
Enzyme B
Substrate
(a)
Cyanogenic glucoside
Hydrogen cyanide
What are the phenotypes (cyanogenic or non-cyanogenic) of the following genotypes?
Explain your answer.
(i)
AABb
...........................................................................................................................
...........................................................................................................................
(ii)
aaBB
...........................................................................................................................
...........................................................................................................................
(3)
(b)
Two clover plants, each with the genotype AaBb were crossed.
(i)
Use a genetic diagram to show the genotypes of the offspring.
(ii)
What is the expected ratio of cyanogenic to non-cyanogenic plants in the offspring?
...........................................................................................................................
(3)
(c)
Cyanogenic clover plants are toxic to slugs. Slugs are common at low altitude but not at
high altitude where the climate is colder. When the cells of cyanogenic clover plants freeze,
the hydrogen cyanide that is released kills the cells and as a result the plant dies. The
frequencies of the alleles for cyanogenesis are different in clover plants growing at low and
at high altitudes.
(i)
How would you expect the allele frequencies to differ?
...........................................................................................................................
...........................................................................................................................
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Sir George Monoux Sixth Form College
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(ii)
Use the information given to explain how the different allele frequencies might be the
result of natural selection.
...........................................................................................................................
...........................................................................................................................
...........................................................................................................................
...........................................................................................................................
...........................................................................................................................
...........................................................................................................................
...........................................................................................................................
...........................................................................................................................
...........................................................................................................................
...........................................................................................................................
...........................................................................................................................
...........................................................................................................................
(6)
(Total 12 marks)
42.
The purple saxifrage is a flowering plant found in the Arctic. It has two distinct forms, one
growing on dry ridges, the other in the valleys.
 On dry ridges, where the temperature is higher and the growing season longer, the plants
grow in upright tufts. These plants are drought tolerant and store carbohydrate which they
use in times of stress.
 In the valleys, where it is colder and the growing season is shorter, the plants grow very
close to the ground. These plants have a higher rate of photosynthesis and grow more
rapidly.
Both forms usually complete their life cycle in the short Arctic summer. In unfavourable years,
plants in the valleys may produce pollen but are unable to form seeds. Some pollen from the valley
plants fertilises plants on the ridges. The seeds may then be washed down to the valleys. Those
that develop and complete their life cycles are all low-growing plants. When plants from the ridges
and the valleys are grown under identical conditions in the laboratory, they have the same growth
form as they did when in their original environment.
(Reproduced from The Biologist, R. M. M. Crawford by permission of Institute of Biology)
(a)
What is the evidence in the passage that the two forms of the purple saxifrage
(i)
are genetically different;
..........................................................................................................................
..........................................................................................................................
(1)
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Sir George Monoux Sixth Form College
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(ii)
belong to the same species?
..........................................................................................................................
..........................................................................................................................
(1)
(b)
When cross pollination between the low-growing and upright forms occurs, both forms of
plant develop when the seeds produced are grown in the laboratory. Explain why only
low-growing plants develop from the seeds which are washed from the ridges into the
valleys.
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
(2)
(c)
Under the conditions described, the two forms of the purple saxifrage are unlikely to evolve
into separate species. Explain why.
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
(2)
(d)
The effect of global warming on the environment of the Arctic is uncertain. Suggest why
species such as the purple saxifrage are likely to survive even if changes in climate do
occur.
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
(2)
(Total 8 marks)
Sir George Monoux Sixth Form College
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43.
The allele for Rhesus positive, R, is dominant to that for Rhesus negative, r.
Haemophilia is a sex-linked condition. The allele for haemophilia, h, is recessive to the allele for
normal blood clotting, H, and is carried on the X–chromosome.
The diagram shows the Rhesus blood group phenotypes in a family tree where some individuals
have haemophilia.
male affected with haemophilia
unaffected male
1
2
Rhesus
positive
3
4
Rhesus
positive
Rhesus
positive
5
6
Rhesus
positive
Rhesus
positive
8
Rhesus
negative
unaffected female
Rhesus
negative
7
Rhesus
positive
9
10
Rhesus
positive
Rhesus
positive
11
Rhesus
positive
12
Rhesus
negative
(a)
(i)
Use the information in the diagram to give one piece of evidence that the allele for
the Rhesus negative condition is recessive.
..........................................................................................................................
..........................................................................................................................
(1)
(ii)
Explain the evidence from the cross between individuals 3 and 4 that the gene
controlling Rhesus blood group is not sex-linked.
..........................................................................................................................
..........................................................................................................................
(2)
(b)
Give the full genotype of
(i)
individual 6;
..........................................................................................................................
(1)
(ii)
individual 12.
..........................................................................................................................
Sir George Monoux Sixth Form College
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(1)
Sir George Monoux Sixth Form College
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(c)
What is the probability that the next child of couple 10 and 11 will have the same genotype
as the first child? Show your working.
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
(3)
(Total 8 marks)
44.
The maps show the present distribution of malaria and the sickle–cell allele in Africa.
Allele frequency
1-10%
Areas
where
malaria
occurs
Sickle-cell allele
Malaria
(a)
10-20%
Draw a genetic diagram to show how sickle-cell anaemia can be inherited from parents who
do not have the condition.
Key to symbols for alleles
HbA
HbS
Normal adult haemoglobin
Sickle–cell haemoglobin
Parental genotypes
Gamete genotypes
Children’s genotypes
Children’s phenotypes
(3)
Sir George Monoux Sixth Form College
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(b)
In a village with a population of 500, there were 8 people who were homozygous for the
sickle–cell allele and 96 who were heterozygous. Calculate the frequency of the HbS allele
in the village. Show your working.
Answer..............................
(2)
(c)
One hypothesis to account for the high frequency of the sickle-cell allele in parts of Africa
concerns resistance to malaria.
(i)
Explain the link between sickle cell anaemia, resistance to malaria and the frequency
of the HbS allele.
...........................................................................................................................
...........................................................................................................................
...........................................................................................................................
...........................................................................................................................
...........................................................................................................................
...........................................................................................................................
...........................................................................................................................
...........................................................................................................................
(3)
(ii)
Select and evaluate the evidence from the maps which supports this hypothesis.
...........................................................................................................................
...........................................................................................................................
...........................................................................................................................
...........................................................................................................................
...........................................................................................................................
(2)
Sir George Monoux Sixth Form College
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(d)
Chloroquine is a drug which has been used very successfully to treat malaria. The use of
chloroquine to treat malaria has produced changes in the frequency of the HbS allele.
Explain how.
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
(2)
(Total 12 marks)
45.
The apple maggot fly (Rhagoletis pomonella) was found originally only on hawthorn trees in
North America. In the 19th century, it spread as a pest to apple trees introduced into North
America by farmers. The flies attacking the apple trees are now genetically different from the flies
that attack hawthorn trees. It is thought that a new species of fly may be evolving.
(a)
Suggest how the flies that feed on apple trees could evolve from those that fed on hawthorn
trees.
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
(3)
Sir George Monoux Sixth Form College
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(b)
Suggest one way in which scientists could find out whether the flies from apple trees were a
different species from those found on hawthorn trees.
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
(2)
(Total 5 marks)
46.
(a)
Explain what is meant by
a recessive allele;
....................................................................................................................................
....................................................................................................................................
a sex-linked gene.
....................................................................................................................................
....................................................................................................................................
(2)
Sir George Monoux Sixth Form College
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(b)
Nail-patella syndrome is an inherited condition caused by a single gene. Sufferers have
abnormal nail growth and underdeveloped kneecaps. The pedigree shows how members of
one family were affected by the syndrome.
Affected
male
1
2
Unaffected
male
Affected
female
3
5
6
7
4
8
9
Unaffected
female
10
Explain one piece of evidence from the pedigree which indicates that
(i)
the allele for the nail-patella syndrome is dominant;
............................................................................................................................
............................................................................................................................
............................................................................................................................
............................................................................................................................
(2)
(ii)
the gene is not sex-linked.
............................................................................................................................
............................................................................................................................
............................................................................................................................
............................................................................................................................
(2)
(Total 6 marks)
Sir George Monoux Sixth Form College
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47.
The diagram shows the range in wing length of a species of small bird on different islands to the
north of Great Britain.
1200
Island 6
900
Distance
north of
600
Great Britain/km
Island 5
Island 4
Island 3
Island 2
300
Island 1
0
45
(a)
(i)
50
55
60
Length of wing/mm
65
70
On which islands might a bird with wings 55mm long live?
............................................................................................................................
(1)
(ii)
What would be the mid-point of the range of wing length expected on an island that is
750km north of Great Britain?
............................................................................................................................
(1)
(b)
In this species wing length increases with body size. Suggest how this trend in body size
might help the birds to survive.
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
(2)
Sir George Monoux Sixth Form College
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(c)
Explain how selection may have resulted in an increase in body size.
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
(3)
(Total 7 marks)
48.
Familial polyposis is a hereditary disease. In this disease small wart-like growths appear on the
inner surface of the large intestine during childhood. The risk that one of these warts will develop
into a malignant tumour in teenage years is so high that affected children are often treated by
having that part of the large intestine surgically removed.
(a)
Suggest one diagnostic technique that could be used to detect familial polyposis in children
from a family with a history of this disease.
....................................................................................................................................
(1)
(b)
Explain what is meant by a malignant tumour.
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
(2)
(c)
Familial polyposis is caused by a dominant allele, A. The allele is not located on a sex
chromosome.
In a couple, the male is heterozygous for familial polyposis and the female is unaffected.
What is the probability that a child born to this couple would have familial polyposis? Use a
genetic diagram to explain your answer.
(3)
Sir George Monoux Sixth Form College
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(d)
Serious diseases caused by dominant alleles are relatively uncommon compared with
diseases caused by recessive alleles.
Suggest an explanation for this.
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
(2)
(Total 8 marks)
49.
Crigler-Najjar (C-N) syndrome is a rare genetic disorder controlled by a recessive allele.
Individuals with the disorder are unable to break down bilirubin, a toxic waste product formed
when the liver destroys old red blood cells. Children with this syndrome must sleep under special
blue lights which destroy bilirubin. If this treatment fails a liver transplant is required.
Although rare in the general population, C-N syndrome is common in one particular community.
This community is described as closed as marriage occurs only between its members.
(a)
Explain what is meant by an allele.
....................................................................................................................................
....................................................................................................................................
(1)
(b)
(i)
Use a genetic diagram to show how two people, neither of whom shows the
disorder, can have a child with C-N syndrome.
(ii)
Suggest how C-N syndrome could become common in a closed community.
............................................................................................................................
............................................................................................................................
............................................................................................................................
............................................................................................................................
............................................................................................................................
............................................................................................................................
Sir George Monoux Sixth Form College
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(4)
Sir George Monoux Sixth Form College
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(c)
Recent studies have shown that it may be possible to repair the defective gene in the liver
cells of affected individuals. Successful gene therapy of all individuals with this disorder in
this community might increase the frequency of C-N syndrome in future generations.
Suggest how.
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
(2)
(Total 7 marks)
50.
In a species of fruitfly, females have two X chromosomes, and males have an X and a Y
chromosome.
A gene controlling eye shape in fruitflies is sex-linked, and found only on the X chromosome.
This gene has two alleles, R for round eyes and B for bar eyes.
A homozygous, round-eyed female (XR XR) was crossed with a bar-eyed male. In the offspring
(Offspring 1), all the female offspring had wide bar eyes (intermediate in size) and all the males
had round eyes.
The figure shows the head of three fruitflies
Wide
bar
eye
(a)
Bar
eye
Round
eye
Name the relationship between the two alleles that control eye shape.
.....................................................................................................................................
(1)
(b)
Give the genotype of the male parent.
.....................................................................................................................................
(1)
Sir George Monoux Sixth Form College
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(c)
Offspring 1 were allowed to interbreed. Complete the genetic diagram to show the
phenotypic ratio you would expect in the resulting Offspring 2.
Parental phenotypes
Parental genotypes
Offspring 1 phenotypes
Round-eyed female
Bar-eyed male
XR XR
Wide bar-eyed female
Round-eyed male
Offspring 1 genotypes
Gametes
Offspring 2 genotypes
Offspring 2 phenotypes
and ratio
(3)
(Total 5 marks)
51.
Thalassemia is a disease in which people homozygous for the recessive allele, t, show a severe
anaemia. Before suitable medical treatment was available, they did not usually survive childhood.
Heterozygotes are only mildly affected, but are more resistant to malaria than people who are
homozygous dominant, TT.
The graph shows the relationship between altitude and the frequency of the thalassemia allele, t,
for a group of villages on the Italian island of Sardinia. The information relates to the early 20th
century.
Sir George Monoux Sixth Form College
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The frequency of the allele t in a population can be calculated from the formula
1
number of Tt genotypes)
2
total number of people
(Number of tt genotypes 
0.24
0.20
0.16
Frequency
of t allele 0.12
0.08
0.04
Carloforte
0
sea
level
(a)
200
400
600
800
1000
Altitude / m
Ignoring the information for the village of Carloforte, describe the relationship between the
frequency of the t allele and altitude.
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
(2)
Until the late 19th century, malaria was commonly found among people living at low altitudes in
Sardinia. It is a serious blood disease caused by a parasite which is carried in the salivary glands of
certain species of mosquito. These mosquitoes, which thrive in warm conditions near to sources of
still or slow-moving water, infect humans with malaria by biting them.
(b)
Suggest an explanation for the higher frequency of the t allele found at certain altitudes.
.....................................................................................................................................
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.....................................................................................................................................
.....................................................................................................................................
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.....................................................................................................................................
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(3)
Sir George Monoux Sixth Form College
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(c)
Information for the village of Carloforte is shown on the graph as a square. This village was
founded more recently, by families from mainland Italy. Suggest two possible reasons for
the unusually low frequency of the t allele found at Carloforte.
1. .................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
2. .................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
(2)
(Total 7 marks)
52.
A species of flowering plant can have white, red or purple flowers. The colour of the flowers is
controlled by two genes. Each gene is found on a different chromosome, and is responsible for one
step in a biosynthetic pathway. The biosynthetic pathway is
gene 1
gene 2
enzyme 1
enzyme 2
J
K
L
colourless
substance
red
pigment
purple
pigment
Gene 1 has the dominant allele A and the recessive allele a. Gene 2 has the dominant allele B and
the recessive allele b. In both cases, the dominant allele needs to be present for the production of
the associated enzyme.
Sir George Monoux Sixth Form College
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(a)
Explain how the two genes are involved in producing white, red or purple flowers.
.....................................................................................................................................
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.....................................................................................................................................
.....................................................................................................................................
(6)
(b)
(i)
A homozygous red-flowered plant was crossed with a homozygous white-flowered
plant. All the flowers of the offspring were purple. What was the genotype of
the red-flowered parent;
...........................................................................................................................
the white-flowered parent?
...........................................................................................................................
(2)
Sir George Monoux Sixth Form College
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(ii)
The purple-flowered offspring were crossed. What phenotypic ratio would you
expect in the next generation? Use a genetic diagram to explain your answer.
(4)
(c)
(i)
Genetically, there are different types of white-flowered plants of this species. Give
their different genotypes.
...........................................................................................................................
(1)
(ii)
You have samples of fresh petals from the two homozygous types of white flowers,
and a pure sample of the red pigment, K. Explain, in outline, how you might
distinguish the two types of petal from each other.
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...........................................................................................................................
...........................................................................................................................
...........................................................................................................................
...........................................................................................................................
(2)
(Total 15 marks)
Sir George Monoux Sixth Form College
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53.
The diagram shows the inheritance of coat colour in pigs through three generations.
1
2
5
3
6
7
12
4
8
9
10
13
14
15
Key: Square = male
Circle = female
11
16
17
18
red
sandy
white
(a)
Explain one piece of evidence from the diagram which shows that coat colour is not
controlled by one gene with two codominant alleles.
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....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
(3)
Two hypotheses were put forward to explain the results, each based on the action of two pairs of
alleles.
Hypothesis 1
Hypothesis 2
Phenotype
Genotype
Genotype
Red
A_B_
A_B_ or A_bb
Sandy
A_bb or aaB_
aaB_
White
aabb
aabb
( _ represents either a dominant or a recessive allele of the gene)
Sir George Monoux Sixth Form College
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(b)
Assuming that Hypothesis 1 is correct, give one possible genotype for each of the following
individuals in the diagram.
11 .....................................................
10 .....................................................
2 .......................................................
(2)
(c)
Explain one piece of evidence from the diagram which shows that Hypothesis 2 should be
rejected.
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
(2)
Sir George Monoux Sixth Form College
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(d)
Individual 18 was crossed with a pig of genotype Aabb.
Use Hypothesis 1 to predict the genotypes and the ratio of phenotypes expected in the
offspring of this cross.
Individual 18
Parental
genotypes
.................................
Other parent
Aabb
Parental
gametes
Offspring
genotypes
Offspring
phenotypes
Expected ratio
of offspring
phenotypes
(4)
(Total 11 marks)
Sir George Monoux Sixth Form College
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54.
The diagram shows the chromosomes from a plant cell in which 2n = 4. The plant is heterozygous
for two characteristics:
 height (the alleles T = tall and t = dwarf);
 flower colour (the alleles B = blue and b = white);
Allele T is dominant to allele t and allele B is dominant to allele b.
Chromatid
T
Centromere
(a)
(i)
T
t
t
b
b
B
B
In the space below, draw a diagram to show the appearance of these chromosomes
just as they are beginning to separate in the first stage of meiosis.
(2)
(ii)
Give all the different genotypes of the gametes produced at the end of meiosis in this
plant.
..........................................................................................................................
(1)
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The plant is also heterozygous for another characteristic, the colour of its stem. The alleles
responsible (A = purple stem, a = green stem) are carried on the same pair of chromosomes as the
alleles for height. Allele A is dominant to allele a. The pair of chromosomes is shown in the
diagram.
T
A
T
A
t
t
a
a
The plant was crossed with a dwarf, green-stemmed plant and produced a large number of
offspring. The table shows the results.
(b)
Phenotype
Tall, purplestemmed
Tall, greenstemmed
Dwarf, purplestemmed
Dwarf,
green-stemme
d
Number of
offspring
91
9
11
89
(i)
Explain how crossing over accounts for the fact that the offspring include some
individuals which are tall and green-stemmed and some which are dwarf and
purple-stemmed.
..........................................................................................................................
..........................................................................................................................
..........................................................................................................................
..........................................................................................................................
..........................................................................................................................
(2)
(ii)
Suggest why there are fewer offspring with these phenotypes.
..........................................................................................................................
..........................................................................................................................
(1)
Sir George Monoux Sixth Form College
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(iii)
When observing dividing cells under a microscope, how would you recognise that
crossing over had taken place?
..........................................................................................................................
..........................................................................................................................
(1)
(c)
Give two factors, other than crossing over, which result in genetic variation in the offspring
produced by a sexually reproducing organism. In each case, explain how the factor brings
about genetic variation.
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....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
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(4)
(Total 11 marks)
55.
The male peacock has very long, brightly coloured tail feathers decorated with ‘eye spots’. The
drawing shows a male peacock displaying to a female.
Sir George Monoux Sixth Form College
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S
There is variation in the number of eye spots on the tails of male peacocks. A positive correlation
exists between the number of eye spots and the number of females that a male mates with. Suggest
how natural selection may have produced an increase in the number of eye spots over time.
...............................................................................................................................................
...............................................................................................................................................
...............................................................................................................................................
...............................................................................................................................................
...............................................................................................................................................
...............................................................................................................................................
...............................................................................................................................................
(Total 3 marks)
56.
(a)
Explain what is meant by
(i)
a recessive allele;
..........................................................................................................................
..........................................................................................................................
(ii)
codominant alleles.
..........................................................................................................................
..........................................................................................................................
(2)
(b)
Chickens homozygous for black feathers were crossed with chickens homozygous for white
feathers. These colours are determined by alleles of a single gene. All the F1 offspring had
blue feathers.
When the blue-feathered F1 chickens were crossed with each other, there were
black-feathered, white-feathered and blue-feathered chickens in the F2 offspring.
(i)
Complete the genetic diagram to explain. how the F1, and F2 phenotypes were
produced.
Parental phenotypes
Parental genotypes
Sir George Monoux Sixth Form College
Black-feathered
FBFB
White-feathered
FWFW
98
F1 genotype
F1, gametes
F2 genotypes
F2 phenotypes
Black-feathered
White-feathered
Blue-feathered
(4)
(ii)
The number of black-feathered, white-feathered and blue-feathered chickens in the
F2 offspring was counted. The observed ratio of black : white : blue was similar to the
ratio expected from theory but not the same. Explain why observed ratios are often
not the same as the expected ratios.
..........................................................................................................................
..........................................................................................................................
..........................................................................................................................
..........................................................................................................................
(2)
(Total 8 marks)
57.
(a)
Explain how natural selection produces changes within a species.
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(4)
Sir George Monoux Sixth Form College
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(b)
Malaria is caused by a parasite that attacks red blood cells, producing repeated bouts of
serious illness and often causing death. The allete for normal haemoglobin in red cells is
HbA. In the West African country of Burkina Faso, twenty percent of people are
heterozygous for a different allele, HbC, which has no effect on their health. People
homozygous for HbC suffer a very mild anaemia. The bar chart shows how the HbC allele
affects the chance of getting malaria.
80
70
Percentage of
60
people with
malaria compared 50
to HbAHbA
40
genotype
30
20
10
0
HbA Hb C
HbC Hb C
Genotype
(i)
Use the bar chart to describe how the HbC allele affects the chance of getting malaria.
..........................................................................................................................
..........................................................................................................................
..........................................................................................................................
..........................................................................................................................
(2)
(ii)
Malaria is very common in Burkina Faso. The HbC allele is increasing in frequency
in this part of Africa. Suggest an explanation for this.
..........................................................................................................................
..........................................................................................................................
..........................................................................................................................
..........................................................................................................................
(2)
(Total 8 marks)
Sir George Monoux Sixth Form College
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58.
Small clearings in woods may occur when large trees die or are blown down. This allows
herbaceous plants to grow for a few years. One plant species that commonly colonises woodland
clearings is the foxglove.
(a)
Name and describe the ecological process which will result in the disappearance of
foxgloves from a clearing after a few years.
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(3)
S
(b)
The foxglove is a biennial plant, which means that it lives for two years. In the first year it
produces leaves but no flowers. In the second year it flowers and each plant releases about
300 000 very small seeds.
(i)
Suggest how being a biennial enables a foxglove plant to produce very large numbers
of seeds.
..........................................................................................................................
..........................................................................................................................
..........................................................................................................................
..........................................................................................................................
(2)
(ii)
Suggest how producing large numbers of very small seeds adapts the foxglove for
colonising woodland clearings.
..........................................................................................................................
..........................................................................................................................
..........................................................................................................................
..........................................................................................................................
(2)
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(c)
The leaves of foxgloves contain a poisonous substance, called digitalis. In high
concentrations, digitalis slows down the rate at which impulses pass across the atria of the
heart.
Explain how the presence of digitalis may protect foxgloves from being eaten by mammals.
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(3)
(Total 10 marks)
59.
(a)
Explain what is meant by
(i)
an allele;
..........................................................................................................................
..........................................................................................................................
(ii)
a sex-linked gene.
..........................................................................................................................
..........................................................................................................................
(2)
(b)
Becker muscular dystrophy is an inherited condition caused by an allele of a gene. Sufferers
experience some loss of muscle strength. The diagram shows how members of one family
were affected by the condition.
1
Affected
male
2
Unaffected
male
3
6
7
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8
9
Unaffected
female
5
10
11
102
(i)
Explain one piece of evidence from the diagram which shows that the allele for
Becker muscular dystrophy is recessive.
..........................................................................................................................
..........................................................................................................................
..........................................................................................................................
..........................................................................................................................
(2)
(ii)
The allele for Becker muscular dystrophy is sex-linked. Explain how individual 9
inherited the condition from his grandfather.
..........................................................................................................................
..........................................................................................................................
..........................................................................................................................
..........................................................................................................................
(2)
(Total 6 marks)
60.
Seeds were obtained from a species of grass growing in a field (Group F) and from the same
species growing on the waste tip of an old copper mine (Group M). Both seed samples were
grown in soil containing high concentrations of copper. After a set time, the height of the grass
plants was measured to the nearest millimetre. The results are shown in the histograms.
50
Plants grown from seeds
from field grass (Group F)
Number 40
of
30
plants
20
10
0
10 20 30 40 50 60 70 80 90 100 110 120 130 140 150
Plant height / mm
15
Plants grown from seeds
from mine-waste grass
(Group M)
Number
10
of
plants
5
0
10 20 30 40 50 60 70 80 90 100 110 120 130 140 150
Plant height / mm
Sir George Monoux Sixth Form College
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(a)
Describe the growth of Group F and Group M plants when grown in soil containing high
concentrations of copper.
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
(2)
(b)
Suggest an explanation for the difference in growth between Group F and Group M
plants.
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
(2)
(c)
Suggest an explanation to account for the one Group F plant that grew to 110-119 mm.
.....................................................................................................................................
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.....................................................................................................................................
(2)
(Total 6 marks)
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61.
Answers should be written in continuous prose, where appropriate.
Quality of Written Communication will be assessed in these answers.
In California there are different types of Ensatina eschscholtzi, each with a characteristic
appearance and found in its own area. They are sufficiently different from each other to be
classified as subspecies. These may become new species with time. The map shows the
distribution of populations of four subspecies.
Ensatina
eschscholtzi
oregonensis
Mountain
ranges
E.eschscholtzi platensis
E.eschscholtzi
xanthoptica
X
(i)
Suggest how speciation may be occurring in these salamanders.
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(4)
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(ii)
Suggest one way in which scientists could find out whether the salamanders from the area
marked X were a different species from those found in other areas.
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
(2)
(iii)
Within each subspecies there is a range of phenotypes. Explain the factors that give rise to
this variation.
.....................................................................................................................................
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.....................................................................................................................................
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.....................................................................................................................................
.....................................................................................................................................
(4)
(Total 10 marks)
62.
A sex-linked gene controls fur colour in cats. Ginger-coloured fur is controlled by the allele G, and
black-coloured fur is controlled by the allele g. Some female cats have ginger and black patches of
fur. They are described as tortoiseshell. Male cats cannot be tortoiseshell.
(a)
What is meant by a sex-linked gene?
.....................................................................................................................................
.....................................................................................................................................
(1)
(b)
A male cat with the genotype Xg Y mates with a tortoiseshell female.
(i)
Give the phenotype of the male.
...........................................................................................................................
(1)
(ii)
Give the genotype of the tortoiseshell female.
...........................................................................................................................
(1)
Sir George Monoux Sixth Form College
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(iii)
Complete the genetic diagram to show the genotypes and the ratio of phenotypes
expected in the offspring of this cross.
Parents
Male
Parental
genotypes
Xg Y
Tortoiseshell female
………………
Parental
gametes
Offspring
genotypes
Offspring
phenotypes
Ratio
(3)
Sir George Monoux Sixth Form College
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(c)
The effect of the G and g alleles is modified by another gene. This gene is not sex-linked
and it has two alleles. The allele d changes the ginger colour to cream and the black colour
to grey. The dominant allele D does not modify the effect of G or g.
A cream-coloured male cat mated with a black female whose genotype was XgXg Dd. Male
kittens of two different colours were produced. Complete the genetic diagram.
Parental
phenotypes
Cream-coloured
male
Black
female
Parental
genotypes
………………
XgXg Dd
Parental
gametes
Male kitten
genotypes
Male kitten
colours
(3)
(Total 9 marks)
63.
In an attempt to control the huge numbers of an insect pest, low doses of a pesticide were sprayed
on a lake. After spraying, the concentration of pesticide in the lake water was 14 parts per billion.
After spraying, diving birds which fed on small fish in the lake were found to be dying. The
concentration of the pesticide in these birds was more than 1 part per thousand.
(a)
Explain why the pesticide was in such a high concentration in the diving birds.
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
(3)
Sir George Monoux Sixth Form College
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S
(b)
The lake was sprayed three times. The first spraying killed almost all of the insects, as did a
second application five years later. When the lake was treated for a third time it was found
that some insects were resistant to the pesticide.
Explain how resistance to the pesticide evolved in the insect population.
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
(3)
S
(c)
This pesticide is able to pass easily through cell membranes. Suggest why.
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
(2)
(Total 8 marks)
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64.
(a)
A protein found on red blood cells, called antigen G, is coded for by a dominant allele of a
gene found on the X chromosome. There is no corresponding gene on the Y chromosome.
The members of one family were tested for the presence of antigen G in the blood. The
antigen was found in the daughter, her father and her father’s mother, as shown in the
genetic diagram below. No other members had the antigen.
Grandmother
(has antigen G)
Genotypes ……… or ………
Gamete
genotypes
……… or ………
Grandfather
Grandmother
…………
…………
…………
…………
…………
…………
Father
(has antigen G)
Genotypes
Grandfather
Mother
……… ………
Gamete
……… ………
genotypes
Daughter
(has antigen G)
Genotype ………
(i)
One of the grandmothers has two possible genotypes. Write these on the genetic
diagram, using the symbol XG to show the presence of the allele for antigen G on the
X chromosome, and Xg for its absence.
(1)
(ii)
Complete the rest of the diagram.
(3)
(iii)
The mother and father have a son. What is the probability of this son inheriting
antigen G? Explain your answer.
Probability .....................................................
......................................................................................................................….
......................................................................................................................….
(2)
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(b)
During meiosis, when the X and Y chromosomes pair up, they do not form a typical
bivalent as do other chromosomes. Explain why.
................................................................................................................................….
....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
(2)
(Total 8 marks)
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