Question

Colorblindness is an X-linked recessive trait. A phenotypically normal man and a colorblind woman have four sons.

A. 0
B. 1/2
C. 1/4
D. 1/8
E. 1/1

Answer 1

All sons of a colorblind woman and a non-colorblind man will be colorblind, as they inherit the X-linked recessive allele for colorblindness from the mother and a Y chromosome from the father, making the probability 1/1 or 100%.

Step-by-step explanation:

Colorblindness is an X-linked recessive trait, which affects males more frequently than females because males have only one X chromosome. In the scenario provided, a phenotypically normal (not colorblind) man and a colorblind woman have children, and we are concerned with determining the probability of their sons being colorblind. Since the mother is colorblind, she must carry two alleles for colorblindness (XcXc).

The father, being normal, has one X chromosome without the colorblind allele (XY). Therefore, all male offspring will receive a Y chromosome from the father and an Xc chromosome from the mother, resulting in them all being colorblind. Hence, the correct answer to the chance of the sons being colorblind is E. 1/1 or 100%.