Hemophilia is a recessive trait linked to the X chromosome. Albinism is an autosomal recessive trait.

Hemophilia is a recessive trait linked to the X chromosome. Albinism is an autosomal recessive trait. A married couple, normal in these characteristics, had a child with both anomalies. What is the probability of a healthy child being born in this family?

Let’s designate as H allele of the gene, which corresponds to the healthy state of blood coagulation systems, and h – allele corresponding to hemophilia. Let us denote by the letter a and A, respectively, the recessive allele of albinism and the dominant allele of normal color. It must be remembered that the father has only one copy of the gene responsible for blood clotting (the Y chromosome is small and does not contain a second copy). If a couple has a sick child, then they are not homozygous for allele A, and the mother has a recessive h, that is, they have the following genotypes: mother Hh Aa, father HY Aa. According to the rule of gamete purity, only 1 allele of each gene gets into each gamete.
The crosses are sick, the ovals are healthy. We divide 9 healthy people by 16 patients – the probability of a healthy birth is 0.5625.