Multiple alleles : More than two alternate forms of a gene present on the same locus of a homologous pair of chromosomes in a population are called multiple alleles. They control the single trait. For example, ABO blood group in humans.
Pleiotropic genes : The gene having multiple phenotypic effects because of its ability to control the expression of a number of characters is called pleiotropic gene. For example, skin pigmentation and phenylketonuria.
