multiple alleles

A single individual carries at most two alleles of a gene — one on each homologous chromosome. But across a whole population, a gene may exist in many different versions. 'Multiple alleles' describes exactly this: a gene with three or more variant forms circulating among individuals.

Think of it like shoe styles in a shop: any one person wears a single pair, but the shelf may hold dozens of designs. Likewise, although you personally hold only two alleles at a locus, the species' gene pool can contain a whole catalog of alternatives, each differing slightly in DNA sequence.

Multiple alleles widen the range of possible genotypes and phenotypes, since each pairing of two alleles from the larger set is a different combination. The dominance relationships among them can be intricate, with some alleles dominant to one another and some codominant — the ABO blood group is the classic illustration with its three main alleles.