In Labradors two genes interact to determine coat color BB h

In Labradors, two genes interact to determine coat color. BB homozygotes and Bb heterozygotes are black, while bb homozygotes are brown. The second gene, E, is epistatic over the B gene, and ee homozygotes always have yellow fur. If you crossed a brown Labrador (bb Ee genotype) with a yellow Labrador (Bb ee genotype), what would be the expected phenotypic ratios of their progeny? Assume that the two genes are unlinked.

Solution

If we assume that the genes are unlinked, then when we will cross the genotypes bbEe and Bbee genotypes, would get the following genotypes- BbEe, Bbee,bbEe and bbee.Since, ee homozygotes always have a yellow colour and it is mentioned that the gene E is epistatic over the B gene, 50% of the progeny should have yellow fur, 25% should have black fur and rest of the 25% should have brown fur. In this case, Mendel\'s epistatic ratio of 9:3:3:1 is not expected to be maintained since the gene is epistaic over the other and also controls fur colour..