Part B - Lethal alleles and epistasis In addition to A and a, the “agouti” gene

Because the presence of the AY allele is epistatic to (masks expression of) the B/b gene, the B/b gene does not need to be taken into consideration in this problem. For the AYa x AYa cross, 1/4 of the offspring would have the AYAY genotype, which is lethal before birth. For the live-born offspring, 2/3 would be AYa, and thus have yellow fur.

The effect of a fourth gene on fur color

In the same mouse species, a fourth unlinked gene (gene P/p) also affects fur color.•For mice that are either homozygous dominant (PP) or heterozygous (Pp), the organism’s fur color is dictated by the other three genes (A/a, B/b, and C/c).
•For mice that are homozygous recessive (pp), large patches of the organism’s fur are white. This condition is called piebaldism.

In the same mouse species, a fourth unlinked gene (gene P/p) also affects fur color.•For mice that are either homozygous dominant (PP) or heterozygous (Pp), the organism’s fur color is dictated by the other three genes (A/a, B/b, and C/c).
•For mice that are homozygous recessive (pp), large patches of the organism’s fur are white. This condition is called piebaldism.
 


In a cross between two mice that are heterozygous for agouti, black, color, and piebaldism, what is the probability that offspring will have solid black fur along with large patches of white fur? (Hint: Consider each gene separately; then use the multiplication rule. For more help getting started, see Hint 1.)
Express your answer as a fraction using the slash symbol and no spaces (for example, 3/16).