Pleiotropy is the effect of a single gene on more than one characteristic. Examples : 1. The "frizzle-trait" in chickens. The primary result of this gene is the production of defective feathers. Secondary results are both good and bad, good include increased adaptation to warm temperatures, bad include increased metabolic rate, decreased egg-laying, changes in heart, kidney and spleen. 2. Cats that are white with blue eyes are often deaf, white cats with a blue and an yellow-orange eye are deaf on the side with the blue eye. 3. Sickle-cell anemia is a human disease originating in warm lowland tropical areas where malaria is common. Sickle-celled individuals suffer from a number of problems, all of which are pleiotropic effects of the sickle-cell allele.