Question

A woman is phenotypically normal, but her father had the sex-linked recessive condition of red-green color blindness. If she has children with a man with normal vision, what is the probability that their first child will have normal vision and their second child will be color blind?

a) 1/4
b) 1/2
c) 3/4
d) 1

Answer 1

The probability that a female carrier of red-green color blindness and a male with normal vision will have a first child with normal vision and a second child who is colorblind is 1/8 if the second child is a son.

Step-by-step explanation:

The question concerns the probability of inheriting sex-linked traits such as red-green color blindness. Since red-green color blindness is X-linked and the woman has a colorblind father but is phenotypically normal, she must be a carrier of the colorblind allele. A male with normal vision will only provide a normal X chromosome to a daughter or a normal Y chromosome to a son.

For their first child to have normal vision, a son must inherit the mother's normal X chromosome or a daughter must inherit the mother's normal X chromosome and the father's normal X or Y. For their second child to be colorblind, a son would have to inherit the mother's X chromosome with the colorblind allele.