Individuals with a genetic defect in phenylalanine hydroxylase require an additional amino acid in their diet which is not an essential amino acid in the ordinary human diet. Which nonessential amino acid has become essential because of the lack of phenylalanine hydroxylase

Tyrosine.

Explanation:

Tyrosine is a non-essential amino acid, it is part of proteins and is considered an aromatic amino acid. Its synthesis occurs from the hydroxylation of phenylalanine as long as it contains an adequate supply of this amino acid.Phenylketonuria is a hereditary disease whose main treatment is dietary restriction of the amino acid phenylalanine. People with phenylketonuria may have low levels of the amino acid tyrosine in their blood.Phenylalanine hydroxylase is an enzyme that converts phenylalanine to tyrosine. Deficiency of the enzyme phenylalanine hydroxylase is a congenital error of metabolism.

chordata is the answer