43.3k views
1 vote
in labrador retrievers, there is recessive epistasis between the e and b genes, both of which influence coat color. from a cross between two dihybrid labs (bbee), what proportion of the offspring should have yellow coats?

1 Answer

5 votes

Final answer:

From a cross between two dihybrid Labrador Retrievers (Bbee), the proportion of offspring with yellow coats is 1/4. This calculation takes into account recessive epistasis, where the presence of the ee genotype results in a yellow coat, irrespective of the B allele's expression.

Step-by-step explanation:

In Labrador Retrievers, fur color is influenced by epistasis involving two genes with alleles E and B. Specifically, the e allele displays recessive epistasis, meaning that when an individual has two copies of this allele (ee), it will have a yellow coat, regardless of the B allele's configuration. Black labs are produced by the B_E_ genotype and chocolate labs by the bbE_ genotype. From a cross between two dihybrid Labradors (Bbee), the proportion of offspring with yellow coats can be calculated using the 9:3:3:1 dihybrid cross ratio.

However, because the e gene is epistatic to the B gene, any offspring with the homozygous recessive genotype (ee) will be yellow, irrespective of the B gene's expression. Consequently, to determine the number of offspring with yellow coats, we would only need to consider the e gene. The cross Bbee x Bbee results in offspring with the following proportions: 9/16 with the B gene expressed (either black or chocolate depending on B or b), 3/16 with the bb genotype (chocolate, because they are not ee), and 4/16 with the ee genotype (which will all be yellow truly because of recessive epistasis by e). Thus, 4/16 or 1/4 of the offspring are expected to have yellow coats.

User Parakh
by
8.7k points
Welcome to QAmmunity.org, where you can ask questions and receive answers from other members of our community.

9.4m questions

12.2m answers

Categories