What is pleiotropy? Explain with an example.

(N/A) Pleiotropy is a phenomenon where a single gene influences two or more seemingly unrelated phenotypic traits. Such genes that affect multiple traits are called pleiotropic genes.
In many cases,the mechanism of pleiotropy occurs because a gene affects a metabolic pathway,which subsequently leads to various phenotypic expressions.
An example of this in humans is Phenylketonuria $(PKU)$. This disorder is caused by a mutation in the gene that codes for the enzyme phenylalanine hydroxylase. This single gene mutation results in multiple phenotypic expressions,including mental retardation and a reduction in hair and skin pigmentation.
Additional Information:
In Drosophila,the recessive gene responsible for vestigial wings also affects other traits: $(i)$ structure of the spermatheca,(ii) bristles,(iii) reduced egg production,and (iv) halteres (balancing organs).