Question

phenylketonuria (pku) is a human disease that requires two recessive genes to appear in an individual. which of the following is definitely true of the parents of a child suffering from pku? one parent must have suffered from pku. the grandparents on their mothers side suffered from pku. both parents must have carried at least one gene for pku. neither parent suffered from pku.

Explanation:

PKU is a recessive - trait disease. A child with PKU has two recessive genes. Each parent must have contributed one of these recessive genes, meaning both parents carried at least one PKU - related recessive gene. A parent doesn't have to have the disease themselves to pass on the gene (they could be carriers). There's no information to suggest grandparents on the mother's side had the disease, and it's not necessary for one parent to have had the disease. Also, it's possible for one or both parents to have had the disease.

Answer:

C. Both parents must have carried at least one gene for PKU.