Question

Colorblindness is an X-linked recessive trait. A couple has a color-blind son and a daughter with normal vision. Which of the following conditions is a likely explanation?

The father was heterozygous for colorblindness
The father was colorblind
The mother was colorblind
The mother was heterozygous for colorblindness
Two of the above

Answer 1

Colorblindness is an X-linked recessive trait. Boys will be colorblind if they inherit the colorblind gene from their mother. Girls can be carriers of the colorblind gene without expressing it.

Step-by-step explanation:

Colorblindness is an X-linked recessive trait. Boys only have one X chromosome, so if that chromosome carries the gene for colorblindness, they will be colorblind. Girls, on the other hand, have two X chromosomes, so they can have one X chromosome with the colorblind gene and one X chromosome with a normal gene for color vision. Since colorblindness is recessive, the dominant normal gene will mask the recessive colorblind gene.