Question

In mice the genotype cc is albino, with C allowing color formation. B is black fur and bb is brown fur. What phenotypic ratio would you expect from crossing Ccbb x Ccbb?

Answer 1

When crossing two mice with genotypes Ccbb, due to the epistatic nature of the C allele over the B allele, we expect a 1:1 phenotypic ratio of colored to albino offspring. All colored offspring will have brown fur, as only b alleles are present for fur color in this cross.

Step-by-step explanation:

Understanding Phenotypic Ratios in Mice Genetics

In mice genetics, the presence of color and the type of fur color are controlled by two different gene loci. The C locus is responsible for pigment production, with cc resulting in an albino mouse, while the B locus determines the fur color — B for black fur and bb for brown fur. When it comes to crossing two heterozygotes with the genotypes Ccbb, the resulting phenotypic ratio would depend on the inheritance of the C allele, since it is epistatic over the B allele.

However, in this specific cross (Ccbb x Ccbb), the offspring can only inherit a b allele from both parents for fur color, leading to all non-albino mice being brown. The possible genotypes for color production are Cc and cc. Hence, a 1:1 ratio of colored to albino mice would be expected, with all colored mice displaying brown fur.