A male and a female are each heterozygous for both cystic fibrosis (CF) and phenylketonuria (PKU). Both conditions are autosomal recessive, and they assort independently.

What proportion of the children of this couple will have neither condition?

Key Concepts

Autosomal Recessive Inheritance

Autosomal recessive inheritance refers to a pattern where two copies of a mutated gene (one from each parent) are necessary for an individual to express a recessive trait. In the case of cystic fibrosis and phenylketonuria, both conditions require that an individual inherits two copies of the mutated gene to exhibit symptoms. If an individual has one normal and one mutated gene, they are considered a carrier but do not show the disease.

Heterozygous Genotype

A heterozygous genotype consists of two different alleles for a particular gene, one inherited from each parent. In this scenario, both parents are heterozygous for cystic fibrosis (CF) and phenylketonuria (PKU), meaning they each carry one normal allele and one mutated allele for these conditions. This genetic makeup is crucial for determining the potential genotypes of their offspring.

Independent Assortment

Independent assortment is a principle of genetics stating that alleles for different traits segregate independently of one another during gamete formation. In this case, the alleles for cystic fibrosis and phenylketonuria assort independently, allowing for a variety of combinations in the offspring. This principle is essential for calculating the probabilities of different genetic outcomes in the children of the heterozygous parents.