Genetics of Phenylketonuria: Phenylketonuria is a genetic defect that exhibits autosomal recessive inheritance. Phenylketonuria: Genetics Information. Genetics of Phenylketonuria: Classical PKU is an autosomal recessive disorder, caused by mutations in both alleles of the gene for phenylalanine hydroxylase (PAH), found on chromosome 12. In the body, phenylalanine hydroxylase converts the amino acid phenylalanine to tyrosine, another amino acid.