(1) The existence together of many forms of DNA sequences at a locus within the population.
(2) A discontinuous genetic variation that results in different forms or types of individuals among the members of a single species.
Genetic polymorphism promotes diversity within a population. It often persists over many generations because no single form has an overall advantage or disadvantage over the others regarding natural selection. A common example is the different allelic forms that give rise to different blood types in humans.