Allele

An allele (from the Greek αλληλος allelos, meaning other) is one of a series of different forms of a gene. The word is a short form of allelomorph ('other form'), which was used in the early days of genetics to describe variant forms of a gene detected as different phenotypes. Alleles are now understood to be alternative DNA sequences at the same physical gene locus, which may or may not result in different phenotypic traits.