All the following are example of pleiotropy except

A single gene can exhibit multiple phenotypic expressions. Such a gene is called a pleiotropic gene. The underlying mechanism of pleiotropy in most cases is the effect of a gene on metabolic pathways which contribute towards different phenotypes. Examples: sickle cell anemia, phenylketonuria and gene for starch synthesis in pea

 Traits are generally controlled by three or more genes and are thus called as polygenic traits.

Skin color in humans is controlled by three genes. polygenic inheritance.