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

Genotypes of all offspring: AABB, 2AABb, 2AaBB, 4AaBb, AAbb, aaBB, 2Aabb, 2aaBb, aabb.

Fraction of the offspring with one of the two dominant alleles by gene А: 2AaBB, 4AaBb, 2Aabb - 50%.

Fraction of the offspring with one of the two dominant alleles by gene B: 2AABb, 4AaBb, 2aaBb - 50%.

Fraction of the offspring with only one of the two dominant alleles: 2Aabb, 2aaBb - 25%.