A normal woman with a color blind father married a color blind man. What is the probability of having healthy children?

It is well known that the gene that causes the development of color blindness is inherited in the structure of the X chromosome. Let’s designate the chromosome with the gene that causes the development of this pathology as X d. A chromosome with a gene that causes a person to develop a normal ability to distinguish colors is denoted as X D.

The father of a woman with color blindness had the X d Y genotype, he produced two types of spermatozoa – Xd and Y and was able to pass on to his daughter only the gene for color discrimination pathology in the X chromosome.

Since a woman, according to the condition of the problem, has normal vision, she is a carrier of the gene for color blindness. She has a heterozygous genotype X D Xd, produces eggs X D and Xd. It transfers both the pathological gene and the gene for normal vision to children.

A man, being color blind, has the X d Y genotype and produces sperm cells X d and Y.

The offspring of this married couple will be represented by the following possible options:

girls with normal vision, but who are carriers of the pathological gene (X D Xd) – 25%;

girls with color blindness (X d X d) – 25%;

boys with normal vision (X D Y) – 25%;

boys with color blindness (X d Y) – 25%.

Answer: the probability of having healthy children in the presented married couple is 50%.