One form of color blindness is inherited as an autosomal recessive trait, while the other is inherited

One form of color blindness is inherited as an autosomal recessive trait, while the other is inherited as a recessive trait linked to the X chromosome. What is the probability (%) of the birth in a family among the sons of a child with any form of color blindness, if the mother and father are healthy, but heterozygous for color blindness genes?

If the father is healthy, and the gene linked to the X chromosome is recessive, he is the carrier of the normal gene. Therefore, the form of color blindness associated with this gene does not threaten his sons.

As for the other recessive gene (let’s designate it as a), the genotypes of heterozygous parents for it will be Aa, and the possible genotypes of children are AA, Aa and aa.

In the latter case, the disease will manifest itself. This will happen with a 33.3% probability.