Question

A man and his wife both have normal color vision, however their daughter is positive for red-green color blindness. The man sues his wife for divorce on the grounds of infidelity. What are the possible genotypes of the man, his wife, and their daughter? Does genetics justify the man’s case?

Answer 1

Answer:

Man's genotype: XᴮY

Woman's genotype: XᴮXᵇ

Daughter's genotype: XᵇXᵇ

The daughter is not the man's child.

Explanation:

Color blindness is a sex-linked trait caused by a recessive allele located in the X chromosome (Xᴮ=normal vision; Xᵇ-color blind).

Women have two X chromosomes, while men have an X and a Y chromosomes. For that reason, women need to have two recessive alleles to be color blind, while men only need one Xᵇ to be colorblind.

Since the man has normal color vision, his genotype would be XᴮY.

If the daughter is her father's, she would have inherited his dominant Xᴮ allele, so she would have normal vision. However, she is colorblind, so her genotype is XᵇXᵇ. She is not the man's daughter.

The mother also has normal color vision, but her daughter inherited a recessive allele from her, so her genotype is heterozygous XᴮXᵇ.