Questions
Q1.
An individual’s eye colour is determined by the alleles they inherit from their parents.
A female parent with the genotype (bb) had blue eyes and a male parent with the genotype (Bb) had
brown eyes.
(i) Complete the Punnett square to show the gametes of the parents and the genotypes of the
offspring.
(2)
(ii) If these two parents have one child, state the probability that this child would have blue eyes.
(1)
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(iii) Give the genetic term that describes the genotype (bb).
(1)
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Q2.
Monohybrid inheritance
Cystic fibrosis is a genetic disorder caused by recessive alleles.
The diagram shows the inheritance of cystic fibrosis in a family.
(a) (i)
State the number of offspring in generation III who will have the disorder cystic fibrosis.
(1)
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(ii) Complete the sentence by putting a cross (
In generation III, individual 3 is
) in the box next to your answer.
(1)
A a carrier of the cystic fibrosis allele
B heterozygous for cystic fibrosis
C homozygous dominant for cystic fibrosis
D homozygous recessive for cystic fibrosis
(iii) Explain why both individuals in generation II must be heterozygous for cystic fibrosis.
(2)
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(b) Complete the Punnett square Complete the Punnett square to illustrate the inheritance of cystic
fibrosis from the two heterozygous parents in generation II.
Use B for the dominant allele and b for the recessive allele.
(2)
(c) Explain why pedigree analysis would be important to the unaffected individuals in generation III.
Use percentages or ratios to help illustrate this.
(2)
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Q3.
Inheritance
The peppered moth (Biston betularia) exists in dark and light forms.
(a) (i) Complete the sentence by putting a cross (img) in the box next to your answer.
Characteristics such as colour are coded for by alleles.
An allele is
(1)
A a single chromosome
B a single gene
C an alternative form of the same chromosome
D an alternative form of the same gene
(ii) The allele for the dark colour is B and is dominant. The allele for the light colour is b and is
recessive.
Complete the table to show all possible genotypes of dark moths.
(2)
possible genotypes of dark moths
(iii) Complete the Punnett square for a cross between a moth heterozygous for colour and a moth
homozygous recessive for light colour.
(2)
%%%
(iv) Give the ratio of light to dark moths in the Punnett square in (a)(iii).
(1)
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*(b) Peppered moths can be eaten by birds.
In areas where there is pollution, trees are covered by dark sooty deposits.
The graphs show the percentages of dark and light coloured moths in the same four
Using the information in the graphs, explain how the peppered moths have been affected by natural
selection.
(6)
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Mark Scheme
Q1.
Question
Number
Answer
Acceptable answers
Mark
(i)
gametes in
male/female
gametes headings
(1) offspring
genotypes (1)
Question
Number
(ii)
0.5 / 50% / 50/50 / ½
/ 2/4 / 2:2 /even
chance
Question
Number
(iii)
Answer
Answer
homozygous
recessive
homozygous
recessive
(2)
Acceptable answers
Mark
evens
(1)
Acceptable answers
Accept any
reasonable spelling
of the term Reject
heterozygous
Mark
(1)
Q2.
Question
Number
(a)(i)
Question
Number
(a)(ii)
Question
Number
(a)(iii)
Question
Number
(b)
Answer
Acceptable answers
Mark
2 / two
Answer
(offspring) 2 and 3
Acceptable answers
(1)
Mark
D
Answer
Acceptable answers
(1)
Mark
An explanation
linking two of the
following points:
• two of the offspring
from generation II
had CF (1) • the
children with cystic
fibrosis must have
inherited 1 recessive
allele from each
parent / children
must have 2
recessive alleles (1)
• both parents must
have 1 recessive
allele / be carriers of
the CF allele (1)
Answer
ORA if homozygous
dominant then no CF
offspring Ignore:
references to genes
ORA if homozygous
recessive offspring
would have CF
Acceptable answers
(2)
Mark
correct gametes (1)
correct offspring (1)
Accept bB instead of
Bb
Question
Number
(c)
Answer
Acceptable answers
An explanation
linking two of the
following points:
• pedigree analysis
will determine the
likelihood that their
offspring could
inherit the CF
allele(1) • if
heterozygous there
is a 50% chance
(that the CF allele)
will be passed on / if
2 heterozygous
parents 25% chance
the offspring will
have CF(1) • if
either parent is
homozygous
dominant there is 0%
chance that their
Accept to see if
they are a carrier of
the CF allele
Accept ratios rather
than percentages 2
in 4 chance
(2)
Mark
(2)
offspring could have
the disease(1)
Q3.
Question
Number
(a)(i)
Question
Number
(a)(ii)
Question
Number
(a)(iii)
Question
Number
(a)(iv)
Question
Number
QWC
Level
1
Answer
D
Answer
Acceptable answers
Mark
Acceptable answers
(1)
Mark
Accept any two of
the genotypes in any
order
Acceptable answers
(2)
Mark
Acceptable answers
(2)
Mark
2:2
e.c.f
Indicative Content
(1)
Mark
*(b)
An explanation to
include some of the
following points
• More light moths
than dark in 1890
• More dark moths
than light in 1990
• There is less
change in region B
compared to the
other regions
• Correct reference
to camouflage/ better
adaptation • 1990
more pollution so
dark coloured trees
• Survival of the
fittest / those seen
by the birds more
likely to be eaten
• Those not eaten
lived to breed
• DNA / allele for
dark colour passed
on • Produced more
dark coloured
offspring
(6)
No rewardable content
• direct reading from the graph without full
explanation • there is some reference to
how the environment affects the numbers of
different coloured moths • the answer
Answer
1 mark for correct
parental gametes 1
mark for correct
offspring
Answer
0
1-2
2
3-4
3
5-6
communicates ideas using simple language
and uses limited scientific terminology
• spelling, punctuation and grammar are
used with limited accuracy
• there is use of the graph and the
candidate indicates a link between pollution
and predation • answer may have sections
missing with candidate correctly identifying
the change in numbers of only one type of
moth • the answer communicates ideas
showing some evidence of clarity and
organisation and uses scientific terminology
appropriately • spelling, punctuation and
grammar are used with some accuracy
• most of the indicative content is included,
explaining a clear link between pollution and
predation rates for both types of moth.
• answer is coherent without missing
sections and information on survival of the
fittest / natural selection is included • the
answer communicates ideas clearly and
coherently uses a range of scientific
terminology accurately • spelling,
punctuation and grammar are used with few
errors