The recessive allele that causes phenylketonuria (pku) is harmful, except when an infant's diet has appropriate levels of the amino acid phenylalanine. what maintains the presence of this harmful allele in a population's gene pool?
a) stabilizing selectionb) heterozygote advantagec) balancing selectiond) diploidye) x

d) diploidy

Explanation:

PKU is a genetic condition caused by changes in genes and are transferred through generations in a recessive inheritance pattern. PKU is caused by mutations in the gene PAH  phenylalanine hydroxylase (PAH)  which codes for an enzyme (type of protein) called phenylalanine hydroxylase. PKU is caused by an Autosomal recessive pattern  i.e A person must have a mutation on BOTH of his/her two copies of the  PAH gene in order to have PKU  and this only occurs if both parents are carriers for PKU.

Now , What maintains the presence of this harmful allele(The recessive allele that causes phenylketonuria (PKU)) in a population's gene pool?

NOTE the word recessive!

The answer is Diploidy.

This is because, the term diploidy refers to a state of having two sets of the chromosomes (and therefore two copies of genes), especially in somatic cells. Therefore, the usefulness of this is to stabilize the chromosome if one of the chromosome(i.e one copy of the gene) is a carrier of PKU.