Pleiotropy = The ability of a single gene to have multiple phenotypic effects

Pleiotropy = The ability of a single gene to have multiple phenotypic effects.

· There are many hereditary diseases in which a single defective gene causes complex sets of symptoms (e.g. sickle-cell anemia).

· One gene can also influence a combination of seemingly unrelated characteristics. For example, in tigers and Siamese cats, the gene that controls fur pigmentation also influences the connections between a cat's eyes and the brain. A defective gene causes both abnormal pigmentation and cross-eye condition.