In humans, color blindness is determined by a recessive gene linked to the X chromosome.

In humans, color blindness is determined by a recessive gene linked to the X chromosome. A man suffering from color blindness marries a woman with normal vision. They have a son who is color blind, determine the genotypes of the parents. what is the probability of having healthy children in this family.

Let’s designate a chromosome containing in its structure a gene that causes the development of a person’s inability to distinguish similar colors as Xd. In this case, the chromosome that determines the development of normal color discrimination will be XD.

A man suffering from this pathology of color discrimination will carry the XdY genotype and produce Xd and Y sperm.He will not pass on the pathological gene to boys, since the male sex of the child is due to the inheritance of the Y chromosome from the father.

Consequently, the color-blind boy born to this pair and written as XdY inherits the color-blind gene from his mother.

The mother has a normal ability to differentiate colors, so she is only a latent carrier of the gene for this color pathology – XDXd. Its body produces eggs XD and Xd.

All possible variants of the offspring of this such family:

healthy girls (XDXd) – 25%;

girls with color blindness (XdXd) – 25%;

color blind boys (XdY) – 50%.

Answer: the probability of having healthy children in a family is 25%.