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  • 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 t

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 ?

Option: 1

1


Option: 2

Nil


Option: 3

0.25


Option: 4

0.5


Answers (1)

best_answer

As we learnt in 

Explanation of law of independent assortment -

Gametes have gene R and r, and they also have alleles Y and y, the segregation of 50% of R and 50% of r is independent from segregation of 50% Y and 50% of y 

- wherein

Thus, there are 4 genotypes of gametes, RY, Ry , rY and ry each with frequency 25% of the total gametes produced. 

 

 

When a colour blind (XcY) marries 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.

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 marry a normal man, 50% of their grandsons will become colour blind

(ii) If carrier daughter marries 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.

So in both the above cases, the result shows 50% of grandsons will be colour blind which in terms of overall progress (son + daughter) comes as 25% thus confirming the probability as 0.25.

Correct option is 3.

Posted by

Ajit Kumar Dubey

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