Question

In a cross of AaBb x AaBb, what fraction of the offspring can be expected to express one of the two dominant alleles, but not both?

Answer 1

Answer: 1/4 (4 out of 16 offsprings express one of the two dominant alleles)

Explanation:

The dominant alleles are A and B

At the end of the cross AaBb x AaBb, 16 offsprings would result. They are as follows: AABB, AABb, AaBB, AaBb

AABb, AAbb, AaBb, AABB,

AaBB, AaBb, aaBB, aaBb,

AaBb, Aabb, aaBb, aabb.

Of all, only 4 offsprings (aaBb, aaBB, AAbb, Aabb) expresses one of the A or B. so 4/16 = 1/4