Q1 07 sp p4 q3 Tt 8 Q2
Tt 8
Q3 05 M/J 06 Tt 9
Q4 O/N 06 Tt 10
Q1 Scallops, which are bivalve molluscs, are important commercially throughout the world.
The marine bay scallop, Agropecten irradians, has three distinct shell colours, yellow,
orange and black. The shell colour is controlled by a gene with three alleles, yellow, Sy,
orange, So, and black, Sb.
Scallops are hermaphrodite and are able to fertilise themselves to produce offspring.
Single mature adult specimens of yellow, orange and black scallops were collected and
kept in separate tanks of seawater until they produced young. The young were then scored
for shell colour. The results were as follows:
yellow scallop – 25 yellow and 8 black
orange scallop – 31 orange and 9 black
black scallop – 27 black
(a) Explain the results from the orange and black scallops, using the symbols given.[6]
(b) Orange scallops are more valued for human consumption.
Describe how a marine biologist could produce a pure-breeding line of orange scallops
for commercial exploitation using the offspring from the single orange scallop.
[2] [Total: 8]
Q2 Colour blindness is a condition characterised by the inability of the brain to perceive
certain
colours accurately.
• The most common form is termed red-green colour blindness (RGC).
• RGC results from a recessive allele.
• 0.6% of females worldwide have RGC.
• 8.0% of males worldwide have RGC.
Fig.
(a) Explain the meaning of the terms allele and recessive. [1 +1]
(b) Explain why females are less likely than males to have RGC. [2]
(c) With reference to Fig. 6.1, and using the symbols R for the dominant allele and r for
the recessive allele, state the genotypes of the individuals 1, 4, 6 and 7. [4] [Total: 8]
Q3 Fig. 2.1 shows the results of experiments investigating the effect of different light
intensities on the rate of photosynthesis of cucumber plants measured as mm3 CO2
uptake per cm2 leaf area per hour. The experiments were carried out at two different
temperatures and two different carbon dioxide concentrations.
Fig.
(a) With reference to Fig.
(i) describe the shape of curve A,[3]
(ii) explain the reasons for the difference between curves B and C. [4]
(b) Suggest two ways in which a commercial grower of cucumbers may increase the
yield of the growing crop.[2] [Total: 9]
Q4 The colour of the tips of the hair in Australian Shepherd dogs is controlled by a gene
at the A locus. There are three alleles at this locus which are:
As Black hair tips
Ay Red hair tips
At Copper hair tips
A cross between two dogs with copper hair tips will always produce offspring with copper
hair tips. A cross between two dogs with black hair tips may produce some offspring with
red hair tips and some with copper hair tips.
(a) State the ratio of offspring phenotypes from the following crosses:
(i) AsAt  AyAy
offspring
phenotypes
ratio .
(ii) AsAt  AtAy
offspring
phenotypes ratio
(iii) AyAt AyAt
offspring
phenotypes ratio [6]
(b) A dog breeder wishes to know whether a dog with red hair tips is either homozygous
or heterozygous for this characteristic.
(i) State the cross needed to determine the dog’s genotype. [1]
(ii) Explain why the offspring of this cross will reveal the genotype of the dog.
[3] [Total: 10]
ANS
Q1 3 (a) Either
If genetic diagram used Penalise once for incorrect symbols
orange dominant to black (for converse);
orange scallop
parents SoSb X SoSb
gametes So Sb So Sb
genotype So So So
Sb So Sb Sb Sb
phenotype orange black
black scallop Sb Sb X Sb Sb
parent
gametes ( Sb Sb )
genotype Sb Sb
phenotype black
Or
If text explanation given
orange dominant to black (or converse);
orange are heterozygous;
(because) ref. 3:1 ratio;
link data to ratio;
black are homozygous;
because all offspring are black; [6]
(b) separate orange scallops produced from first cross/test cross orange with black;
some will produce only orange offspring;
these will be homozygous for orange allele/pure breeding; [2max]
Total: 8
Q2 6 [08]
(a) allele
(different) form of a gene ; A variety / version
ignore refs to locus / mutation [1]
recessive
allele which does not have its effect in heterozygote / allele which (only) has its effect in
homozygote / affects phenotype if dominant allele is absent ; [1]
(b) gene / allele, on X chromosome / sex linkage ;
female, needs 2 RGC alleles / homozygous recessive / can be heterozygous ;
male needs 1 RGC allele ; [2 max
(c) 1 – XRXr / Rr ;
4 – XRY / R / Ro / R- ;
6 – XrY / r / ro / r- ;
7 – XRXr / Rr ; [4]
if X and Y not used then mark to max 3
[Total:8]
Q3 2 (a) (i) at low light intensities ;
rate of photosynthesis is proportional to light intensity / light intensity is
limiting ;
after 1 units of light ;
rate levels off / reaches plateau ;
relevant fig plus units ; [3 max]
(ii) (B) after 3 units light intensity not limiting ;
CO2 now limiting ;
(C) curve continues to increase until 5 units of light ;
light intensity limiting ;
correct description of law of limiting factors ;
detail. collisions of CO2 and enzymes ;
AVP ; e.g., further detail of enzymes [4 max]
(b) optimum temperature ;
method e.g. heaters / ventilation ;
optimum CO2 concentration ;
burners / combustion / add dry ice / pump in CO2 up to 1% ;
high light intensity / longer duration of light / artificial lighting ;
ref. irrigation ;
ref. fertilisers ;
ref. pest / disease control ;
ref. artificial pollination ; [2 max]
[Total: 9]
Q4 (a) (i) black red
1 : 1 ; 2
(ii) black copper red ;
2 : 1 : 1 ; 2
(iii) red copper ;
3 1 ;
2
(b) (i) test / back, cross ;
with, copper / AtAt / homozygous recessive ;
(ii) if all offspring red, homozygous ;
if some offspring copper, heterozygous ;
ref. equal proportions of offspring ; mark (i) and (ii) together 4 max
[Total: 10]