The gene for color blindness is recessive linked to the X chromosome. A dark-haired woman with normal vision

The gene for color blindness is recessive linked to the X chromosome. A dark-haired woman with normal vision, a father who had blond hair and suffered from blindness. Marries a fair-haired man with normal vision. Determine the genotypes of the parents and the likelihood of birth in this family of children of color blindness with dark hair and their gender.

As a rule, a person’s dark hair color dominates over a light one. Let’s designate the gene that causes the development of dark hair in humans as K, then the gene that causes light hair color will be designated as k.

It is known that the gene for color blindness is inherited in the X – chromosome. Let us denote such a chromosome by X d. Then the chromosome with the gene for the color discrimination norm will be X D.

The father of a woman with blond hair and color blindness had the kkX dY genotype. He produced spermatozoa kX d and kY. He passed on genes for recessive traits to his daughter, including the gene for color blindness.

Thus, a healthy dark-haired woman is diheterozygous – Kk X D X d. It produces four types of eggs – K X D, k X d, K X d, k X D.

A man with blond hair and normal color vision has the kk X D Y genotype and produces sperm cells kX D, kY.

The offspring of this married couple includes the following possible options:

healthy girls with dark hair (K kX D X D, K kX D X d);

healthy girls with blond hair (k kX D X d, k kX D X D);

healthy boys with dark hair (Kk X D Y);

boys with color blindness and blond hair (kk X d Y);

boys with color blindness and dark hair (Kk X d Y);

healthy boys with blond hair (kk X D YP).

Children with color blindness and dark hair – 1 in 8, or 12.5%.

Answer: The probability of birth in this married couple of children with color blindness and dark hair is 12.5%.