Previous year MCQs

General science UPPSC 2009 GS-I
Question

A colour-blind man marries a normal woman. The features of colour blindness will appear in his:

Answer & Solution

Answer: (Detailed Solution Below)

Option D: daughter's sons

Detailed Solution:

The correct answer is “daughter's sons ”.
Color blindness is a sex-linked recessive trait. This means that the gene for color blindness is located on the X chromosome. Women have two X chromosomes, while men have one X and one Y chromosome.

If a man is color blind, he has a defective X chromosome. If he marries a normal woman, she will have two normal X chromosomes. Their daughters will inherit one normal X chromosome from the mother and one defective X chromosome from the father. This means that the daughters will be carriers of the color blindness gene but will not be color blind themselves.

However, if a daughter who is a carrier has a son, there is a 50% chance that she will pass the defective X chromosome to her son. If the son inherits the defective X chromosome, he will be color blind.

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