question_answer

Anish is having colour blindness and married to Sheela, who is not colourblind. What is the chance that their son will have the disease?

A)  100%

B)  50%

C)  25%           

D)  0%

Correct Answer: D

Solution :

 Colour blindness is a sex-linked recessive disorder, which results in defects in either red or green cone of an eye which ultimately leads to the failure in discriminating between red and green colour. The gene for colour blindness is located on X-chromosome. Thus, if a colourblind man marries a normal  women the chances for their son to be colourblind is 0% because son will receive X-chromosome from his mother (who is not colourblind) and Y from the father (as gene of colour blindness is present on X, so Y chromosome is not affected at all). Thus, there is no chance for their son to be affected. Infact their girl child (daughter) will be the carrier of the disease. This can be easily illustrated by the cross given below (colourbind father)\[({{X}^{C}}Y\times XX)\] (normal mother)