question_answer

A man whose father was colourblind marries a woman, who had a colourblind mother and normal father. What percentage of male children of this couple will be colourblind? [AIPMT 2014]

A)  25%  

B)  0%    

C)  50%  

D)  75%

Correct Answer: A

Solution :

As colourblindness is a autosomal recessive genetic disorder, for it is present at X-chromosome. Thus, according to the situation given in the question, a man whose father was colourblind (will be, i.e., XY normal) marries a woman whose mother was colourblind and father was normal (i.e., this woman will be a carrier) according to the cross given below Thus, when marriage will happen between a normal man and a carrier woman, in that case percentage of a male child to be colourblind is 25% (this can be easily observed from the cross given below)