question_answer

A woman with normal vision, but whose father was colourblind, marries a colourblind man. Suppose that the fourth child of this couple was a boy. This boy

A)  must have normal colour vision

B)  will be partially colourblind since he is heterozygous for the colourblind mutant allele

C)  must be colourblind

D)  may be colourblind or may be of normal vision

Correct Answer: D

Solution :

Colour blindness is a sex-linked (X-linked) trait. It always transfers from mother to son. A woman whose father was colourblind, will be a carrier to colourblind trait. Marriage of this woman with a colourblind man will result out the above possibilities.