Question:

If a colour blind female marries a man whose mother was also colour blind, what are the chances of her progeny having colour blindness?

Updated On: May 2, 2025

25%
50%
75%
100%

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The Correct Option is D

Solution and Explanation

To determine the probability of progeny having color blindness, we must understand the genetics behind the condition. Color blindness is a sex-linked recessive trait carried on the X chromosome. Let's denote the normal vision allele as X^N and the color blindness allele as X^c.

For a female to be color blind, she must have two copies of the X^c allele (X^cX^c). A male is color blind if he has an X^c allele, as his genotype is X^cY.

The female in this scenario is color blind (X^cX^c), and the male's mother was color blind, meaning he must have inherited the X^c from her. Therefore, his genotype is X^cY.

We will analyze the possible genotypes of their progeny:

A son will inherit an X chromosome from his mother and a Y chromosome from his father.
A daughter will inherit an X chromosome each from both parents.

Parental Genotypes: Female (X^cX^c) and Male (X^cY)

Parents	X^c (Mother)	X^c (Mother)
X^c (Father)	X^cX^c	X^cX^c
Y (Father)	X^cY	X^cY

From this cross, all daughters (X^cX^c) will be color blind, and all sons (X^cY) will be color blind because they inherit the X^c allele. Therefore, 100% of their progeny will be color blind.

The correct answer is 100%.

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