Question

A woman who is a carrier of hemophilia is married with colour blind man. Than what will be the probability of sons to be colorblind..? A) 25% B) 50% C) 75% D) 100% E) None

Answer 1

`E`

Explanation:

In short, colorblindness is an `X` linked recessive disease, so if the father is colorblind, his `X` chromosome is defective, which will never pass to his sons, and so none of the sons will be colorblind.

Below, we are going to study the pedigree in details.

Both colorblindness and haemophilia are `X` linked recessive diseases.

So, the colorblind father will have a genotype of `22 A A + X'Y`(where, `X'` stands for chromosome bearing gene for colorblindness).

While the mother, being a carrier of haemophilia, will have one normal `X` chromosome and one chromosome bearing the gene for haemophilia.

So, her genotype will be `22 A A +XX''` (where, `X''` is representing the chromosome bearing gene for haemphilia).

Below we have worked out the analysis,

We can see out of the `2` daughters, one is carrier of colorblindness and one can be either haemophilic or colorblind, depending on genomic imprinting (which `X` will take the dominant role).

But out of the `2` sons, one is normal and the other is haemophilic.

So, probability of sons to be colorblind is `0%`, and the answer will be `E`.