Principles of Inheritance and Variation — BIOLOGY STD 12 Science — Question

→ We have so far seen the effect of a gene on a single phenotype or trait. There are however instances where a single gene can exhibit multiple phenotypic expression.
→The underlying mechanism of pleiotropy in most cases is the effect of a gene on metabolic pathways which contribute towards different phenotypes.
→ An example of this is the disease phenylketonuria, which occurs in humans.
→ The disease is caused by mutation in the gene that codes for the enzyme phenyl alanine hydroxylase (single gene mutation).
→ This manifests itself through phenotypic expression characterised by mental retardation and a reduction in hair and skin pigmentation.