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 will be carriers of one or both conditions?

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, individuals with one normal and one mutated allele are carriers but do not exhibit symptoms. Understanding this concept is crucial for predicting the genetic outcomes in offspring.

Heterozygosity

Heterozygosity occurs when an individual has two different alleles for a particular gene, such as one normal allele and one mutated allele for cystic fibrosis or phenylketonuria. In this scenario, both parents are heterozygous, meaning they can pass either the normal or mutated allele to their children. This genetic variation is essential for calculating the likelihood of offspring being carriers.

Independent Assortment

Independent assortment is a principle of genetics stating that alleles for different genes segregate independently of one another during gamete formation. In this case, since cystic fibrosis and phenylketonuria are on different chromosomes, the alleles for these traits will assort independently. This concept is vital for determining the genetic combinations possible in the offspring of the heterozygous parents.