Question

Question 3 [15 marks / 15 minutes]

Four alleles of the Agouti gene are known to control coat colour in mice, as shown below. These alleles

form a dominance series: Ay > A > at > a. Ay is also recessive lethal.

Allele Phenotype

Ay yellow

A agouti

at black back, yellow belly

a black

A researcher investigating mouse genetics traps a wild male mouse showing yellow coat colour.

a) If the wild mouse’s coat colour was due to Ay

, describe and explain a single mating experiment

that would identify the mouse’s other Agouti allele.

[7 marks]

When the wild, male yellow mouse was mated to female mice with genotype Ay A, the researcher saw

progeny with the following phenotypes:

Phenotype Number of progeny

yellow 97

agouti 50

b) Use a Punnett square to explain why this result was expected. [8 marks]

Answer 1

a) Ay will give rise to yellow coat color

To find out the other allele of the coat color the Ay male mice mating expriment should be carried out with a female which is homozygous recessive allele, so if the test cross ratio will be 1:1 Then the genotype of the mice trapped heterozygous AyA

mating between AyA and aa genotype (homozygous recessive mice female), the ratio should be 1:1 i.e. 50% will have yellow coat color and 50% will have agouti color(brown).

b) The male Ay yellow when mated with a female mice having genotype AyA will give rise to progeny having both yellow and agouti(brown) coat color in 2;1 ratio . The punnet square is attached below. Since recessive Ay will be lethal so the progeny having AyAy will die.