Question

3.Although there are likely more, there are five major genes that interact to control coat colour in mice. These are: A, B, C, D and S. The A allele produces a phenotype called agouti, which caused by a band of yellow colour on a dark hair shaft. The result is a brindled or salt and pepper appearance. The non-agouti (controlled by the a allele) lacks the yellow band and is a solid black. The B gene controls the colour of the pigment. The B allele codes for black while b codes for brown. In combination with A, the B allele gives black agouti, and solid black when combined with a/a. The combination A/-;b/b produces a streaked brown called cinnamon while a/a; b/b produces solid brown. The C allele permit colour expression while the c allele prevents colour expression. The c/c genotype is epistatic to other colour genes. Animals with a c/c constitution are albinos.The D gene controls the intensity of pigment controlled by other genes. The D/- genotypes permit full expression of pigment, while d/d causes the colour to be diluted or milky (e.g.dilute black). The S gene controls the distribution of pigment or spotting. The genotype S/- results in no spots, while s/s produces spotting called piebald. This pattern can be superimposed on any of the coat colours—with the exception of albino.

Suppose that you crossed mice with the following genotypes: C/c; B/b; A/a; D/d; S/s x C/c; b/b; a/a; D/d; S/s

a. What are the phenotypes of the parental mice?

b. What are the phenotypic ratios and the corresponding generalized genotypes that you expect for the phenotypes listed below?

Solid black

Black agouti

Spotted balck

Dilute black agouti

Brown

Dilute Brown

Cinnamon

Dilute cinnamon

Albino

Answer 1

(a). The phenotypes of parents are C/c; B/b; A/a; D/d; S/s (produces black agouti without spots). And the other combination is C/c; b/b; a/a; D/d; S/s (produces solid brown without spots.)

(b). The phenotypic ratios and the corresponding generalized genotypes:

Solid black=1/2*1/2= 1/4

Black agouti=1/2*1/2= 1/4

Spotted black=1/2*1/2*1/4= 1/4

Dilute black agouti=1/2*1/4= 1/8

Brown=1/2

Dilute Brown=1/2*1/4= 1/8

Cinnamon=1/2*1/2= 1/4

Dilute cinnamon1/2*1/4= 1/8