In organisms, a pleiotropic gene is one that influences more than one trait. Some cats are born with a pleiotropic gene that causes them to have white fur, blue eyes, and deafness.
When scientists first began to understand the basic idea of genetics, most believed that each of an organism's genes affected a single characteristic. Over time, they came to understand that most genes are actually pleiotropic, contributing to multiple traits. Some genetic disorders like Marfan syndrome, which results in tall stature, cardiovascular problems, and long fingers, are caused by a mutation in one pleiotropic gene. Pleiotropic derives from the Greek pleiōn, "greater in quantity" or "very many."