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?

0.5

1

Nil

0.25

Solution

Nil

When a colour blind (X^CY) 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:

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 grand daughter while rest 50% of the grand daughters will be carriers as

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

Some More Questions From Principles of Inheritance and Variation Chapter

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Principles Of Inheritance And Variation

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?

0.5

1

Nil

0.25

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Define heterogamy. Give an example.

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What term is used for the two chromatids resulting from the interchange of segments during crossing over ?

What is name of a cross in which a dominant individual is crossed with a recessive parent?

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Principles Of Inheritance And Variation

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? 0.5 1 Nil 0.25

Some More Questions From Principles of Inheritance and Variation Chapter

Who were the rediscoverers of Mendelism ?

What are the real determinants of what an organism will become ?

What is the unique feature of F1 generation ?

What will be the genetic make up of an organism which suffers from sickle cell anaemia ?

What do the symbols square and circle in a pedigree chart indicate ?

Define heterogamy. Give an example.

How many chromosomes are found in human cells ?

Why is male Drosophila regarded as heterogametic ?

What term is used for the two chromatids resulting from the interchange of segments during crossing over ?

What is name of a cross in which a dominant individual is crossed with a recessive parent?

Mock Test Series

NCERT Sample Papers

Entrance Exams Preparation

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?

0.5

1

Nil

0.25