Question

Explain how a colorblind man and a colorblind woman can have a child with normal vision

Answer 1

He first step in solving this problem requires an examination of the possible genotypes of the parents. As stated color-blindness is a recessive linked trait. So the genotypes of the parents should be:

mother's genotype (normal vision but whose father was color blind) XNXn

She is a carrier because of her heterozygous condition. For the recessive gene to be expressed one must be homozygous for it.

father's genotype (color blind) XnY