question_answer

A colour blind man marries a woman with normal sight who has no history of colour blindness in her family. What is the probability of their grandson being colour blind?                                                      

A)  0.5                 

B)  1                            

C)  Nil                 

D)  0.25                    

Correct Answer: D

Solution :

When a colour blind man (\[{{X}^{C}}Y\]) marries to a woman with normal sight (XX) who has no family history of colour blindness, all of their sons will be normal pure and all of their daughters will be carriers as shown below Normal woman Colour blind man So in the next generation, the children of all of their son will be normal in all conditions (except the case in which the wife involved is not carrier neither colour blind). For carrier daughters. (i) If they many to a normal man 50% of their grandsons will become colour blind as (ii) If carrier daughter marries to a colour blind man 50% of their grandson will be colour blind along with 50% of the granddaughter while rest 50% of the granddaughters will be carriers as So in both the above cases the result shows 50% of grandsons will be colored blind which in terms of overall progenies (son + daughters) comes as 25% thus confirming the probability as 0.25.