If the dominant allele A is necessary for hearing in humans, and another allele, B, located on a different chromosome, results in deafness no matter what other genes are present, what fraction of the offspring of the marriage of aaBb *Aabb will be deaf?
A) none
B) 1/8
C) 1/4
D) 1/2
E) 5/8

Question

Quizplus · Accepted Answer

Given that allele A is necessary for hearing, individuals must have at least one A allele to not be deaf. The B allele causes deafness regardless of other genes. The cross is between aaBb and Aabb individuals. For offspring to be deaf, they can either inherit the b allele from both parents (and not have an A allele from the aa parent) or inherit a B allele from the aaBb parent. The possible genotypes for offspring that would result in deafness include: aaBb, aaBb, aaBB, and aabb. Calculating the probability for each scenario, we find that 5/8 of the offspring will be deaf due to either the presence of the B allele or the absence of the A allele necessary for hearing.

If the Dominant Allele a Is Necessary for Hearing in Humans