the phenomenon in which a single gene is responsible for a number of distinct and seemingly unrelated phenotypic effects
One gene leading to many different phenotypic expressions An excellent example of a gene with pleiotropic effects is the gene for myotonic dystrophy Affected individuals can have one or more of a range of signs and symptoms including characteristic Christmas-tree like cataracts, myotonia, narcolepsy, testicular atrophy, frontal balding, mental retardation, and cardiac abnormalities, among others Source : PhRMA Genomics