Hemophilia in humans is caused by a recessive gene linked to the X chromosome.

Hemophilia in humans is caused by a recessive gene linked to the X chromosome. one healthy son and three healthy daughters were born to healthy parents, and one son turned out to be hemophilic. What is the probability of having children with hemophiliacs and daughters if they marry healthy men?

Since the hemophilia gene is linked to the X chromosome and is recessive, and both parents are healthy, the mother is the carrier of the gene.

Parent genotypes:

father – X (A) Y;

mother – X (A) X (a).

Then the genotypes of their children:

girls – X (A) X (A), X (A) X (a);

boys – X (A) Y, X (a) Y.

Among girls, there are completely healthy X (A) X (A), and there are carriers of the hemophilia gene X (A) X (a).

If female carriers with the X (A) X (a) genotype give birth to children from healthy men with the X (A) Y genotype, the probability of having sick children is 25% (these will be boys). The scheme is the same as that of the parents: a healthy man and a female carrier.