Question

For a pair of genes with alleles: A (dominant) a (recessive) at the first locus; and B (dominant) b (recessive) at the second locus, that operate in a duplicate dominant epistatic manner, what proportion of offspring from a doubly-heterozygous mating are expected to show the recessive phenotype? A. 0.5. B. 1 (it's dominant). C. 15/16. D. 9/16. E. 1/16.

Answer 1

Answer:

E. 1/16

Explanation:

In a duplicate dominant epistasis, when one locus presents a dominant genotype and the other presents a recessive genotype, the dominant one hides the effective of the recessive gene. Therefore, a recessive phenotype will only be observed when both genes are recessive homozygous (aabb).

Assuming a doubly-heterozygous mating (AaBb x AaBb), the probability that both genes are recessive homozygous is:

$P=\frac{1}{2}*\frac{1}{2}*\frac{1}{2}*\frac{1}{2}\\P =\frac{1}{16}$

1/16 of offspring are expected to show the recessive phenotype.