Question

In regard to the baby's colorblindness, a sex-linked recessive trait, you explain that

A) the eggs must have been accidentally switched, since males inherit sex-linked traits only from
their fathers.
B) the baby's father must have a recessive allele for colorblindness.
C) colorblindness often appears randomly, even if neither parent is colorblind.
D) since colorblindness is sex-linked, a son can inherit colorblindness if his mother has the
recessive colorblindness allele.

Answer 1

Colorblindness is a sex-linked recessive trait, requiring females to inherit two colorblindness alleles to be affected. Males inherit colorblindness from their mothers with a single allele, as they have one X chromosome. A colorblind woman indicates both her mother is a carrier and her father is affected by or a carrier of the trait.

Step-by-step explanation:

Colorblindness is a sex-linked recessive trait affecting more males than females due to the differences in their sex chromosomes. For a female to be colorblind, she must inherit two colorblindness alleles, one from each parent. In contrast, males only need to inherit one colorblindness allele from their mothers to be affected, as they have only one X chromosome.

Females have two X chromosomes, and if only one carries the colorblind gene, the other normal gene masks it, turning the female into a carrier without affecting her color vision. Thus, if a woman is colorblind, her father must have the colorblind allele, and her mother must at least be a carrier of the trait.

Also, a son cannot inherit colorblindness from his father because males pass their Y chromosome, not their X, to their sons, and colorblindness is located on the X chromosome.