Question

phenylketonuria (pku) is a disease in humans that results from the abnormal metabolism of the amino acid phenylalanine. if untreated, it can lead to severe brain damage in infants. two normal parents have a child who has pku. what can you determine about the inheritance of the pku allele from this information?
it is pleiotropic.
it is dominant.
it is epistatic.
it is recessive.

Explanation:

• Recessive Trait Indication:
• When two normal parents have a child with a disorder (PKU in this case), it suggests a recessive inheritance pattern. In recessive inheritance, both parents must carry at least one copy of the recessive allele (be carriers) for there to be a chance of their child inheriting two recessive alleles (one from each parent) and expressing the disorder.
• For a dominant trait, if either parent had the dominant allele for the disorder, they would likely express the disorder themselves (assuming complete dominance). Since the parents are normal, it's less likely to be a dominant trait.
• Epistasis involves one gene masking the expression of another gene. There is no information in the question about gene - gene interactions (masking) to suggest an epistatic relationship.
• Pleiotropy is when a single gene has multiple phenotypic effects. The question is focused on the inheritance pattern (how the trait is passed from parents to offspring) rather than the multiple effects of a single gene.

Answer:

It is recessive.