Phenylketonuria is inherited as an autosomal recessive trait. What is the probability of having children

Phenylketonuria is inherited as an autosomal recessive trait. What is the probability of having children with phenylketonuria in a family where the parents are heterozygous for this trait?

Let’s designate the gene that determines the development of phenylketonuria as f, then the corresponding dominant gene that determines the well-being for this disease will be F.

Parents for the phenylketonuria gene are heterozygotes – Ff. Both of them produce eggs and sperm of two types – F – containing and f – containing.

This pair of persons may have offspring of the following options:

healthy children – homozygotes (FF) – 25%;

children with phenylketonuria (ff) – 25%;

healthy children are heterozygotes, carriers of the pathological gene (Ff) – 50%.

Answer: 25%.