PKU is an inherited recessive condition affecting phenylalanine metabolism, managed by identifying affected individuals and controlling diet in inheritance problems.
Coverage 2016–2025 · Updated 16 Jul 2026
Phenylketonuria (PKU) is an autosomal recessive disorder in which mutation reduces the enzyme that converts phenylalanine to tyrosine.
With insufficient enzyme activity, phenylalanine accumulates and tyrosine production is reduced. Two recessive disease alleles are normally required for the affected phenotype.
Genotype → reduced phenylalanine-hydroxylase activity → disrupted phenylalanine-to-tyrosine conversion → altered metabolite concentrations and phenotype.
Restricting dietary phenylalanine lowers the substrate entering the blocked pathway and can reduce the severity of the phenotype.
Diet can change the phenotype but does not remove or rewrite the inherited PKU alleles.
This objective is assessed through essay response, commonly using Explain / Outline.
Explain / Outline
Build the answer around this relationship: PKU is usually autosomal recessive, so carriers can be unaffected.
Representative question
Discuss the causes and treatments of phenylketonuria.
Core D3.2 is secure when the student can move from allele rules into predictions and evidence: gametes form genotypes, genotypes can produce phenotypes, different dominance patterns need different notation, and pedigrees or plots require evidence-based interpretation.
Core inheritance exam questions reward disciplined reasoning. First identify the inheritance rule, then write the correct notation or evidence, then state the phenotype, ratio, or conclusion. This prevents the common mistake of writing definitions without solving the genetic problem.
