Question

Coat colour in Labrador retriever is controlled by epistasis. B specifies black pigment, b is for brown pigment (recessive) and E locus determines the expression of B locus. Which one of the following is wrong?

(a) bb EE gives yellow

(b) Bb EE gives black

(c) bb Ee gives brown

(d) BB EE gives black

This question was addressed to me during an interview for a job.

I would like to ask this question from Epistasis topic in chapter Extension and Deviation from Mendelian Genetic Principles of Cytogenetics

Answer 1

Right choice is (a) bb EE gives yellow

Best explanation: According to the rules of recessive epistasis, at least one dominant allele at the E locus is needed for expression at the b locus. As in option bb EE gives yellow the E locus is dominant so b locus is expressed to give chocolate or brown colour not yellow.