Question

A colour blind man marries a woman with normal sight who has no history of colorblindness in her family . What is the probability of their grandson being colorblind ? A) 0.25 B)0.5 C)1 D)Nil

Answer 1

colourblindness is x linked recessive disorder.Male(XcY) marries a female (XX) who has no history of colourblindness in the family. the progeny produced will be all sons normal and all daughters carrier. when the carrier daughter(XcX) marries a normal male(XY) 50% of sons will be diseased and 50% normal. thus 1in 2 grandson will be diseased thus 0.5