Question

A normal woman whose father was a colour blind, is married to a normal man. The sons would be

• A. 75% colour blind
• B. 50% colour blind
• C. All normal
• D. All colour blind

Answer 1

Answer: (B)

50% colour blind

Colour blindness is a genetic disease which is inherited from the parents to their children. It is a sex linked recessive trait. That is, it encoded on the sex chromosome X; men only have one of them (XY) compared to women (XX) here, if one of the chromosomes is healthy means it won't show up. Each child of a mother affected with an X-linked dominant trait has a 50% chance of inheriting the mutation and thus being affected with the disorder. Since normal woman's father is colour blind, so the chance of getting colour blindness to her daughter is 100% colour blind carriers. If that woman has only one colour blind 'gene' she is known as 'carrier' but she won't be colour blind. When she has a child she will give one of her X chromosomes to the child. If she gives X chromosome with the faulty 'gene' to her son he will be colour blind, but he receives the 'good' chromosome he won't be colour blind. So the sons would be 50% colour blind.

So, the correct answer is option B.