In humans, brown eyes are dominant to blue eyes. If a blue-eyed man has children with a brown-eyed woman whose mother has blue eyes, what percentage of the brown-eyed offspring do you expect will be heterozygous

This question involves a gene coding for eye color in humans. The allele for brown eyes (B) are dominant to blue eyes (b). This means that blue-eyed individual will possess genotype: bb.

According to this question, a blue-eyed man (bb) has children with a brown-eyed woman (B_) whose mother has blue eyes (bb). Since the mother of the brown-eyed woman has a blue eye, this means that the woman will be heterozygous for brown eye (Bb).

Hence, the parents in this question will cross as follows: blue eyed man (bb) × brown-eyed woman (Bb). The offspring/children will have the following genotypes (see attached punnet square); Bb, Bb, bb, bb.

Based on the question, 2/4 = 1/2 of the children will be heterozygous for the eye color trait. That is, ½ × 100 = 50%.