Question

A colorblind man married a woman who wasnt colorblind, but her father had been. The possibility of their first child will be a colorblind girl is

• A. 0 percent
• B. 25 percent
• C. 50 percent
• D. 75 percent
• E. 100 percent

Answer 1

The correct option is B 25 percent

Colorblindness is X-linked recessive disorder and follows criss-cross inheritance. Father ($X^c$Y) of the woman passed the affected X chromosome to her. The genotype of the woman is ($X^c$X) and she is a carrier. The carrier woman forms 1/2 gamete with $X^c$ and 1/2 with X chromosome while the colorblind man forms 1/2 sperms carrying $X^c$ and 1/2 carrying Y chromosome. To have a colorblind daughter ($X^c{X}^c$), possibility of fertilization of 1/2 $X^c$ eggs with 1/2 $X^c$ sperms is 1/4 (25%). Thus, the correct answer is option B.