Allele

An allele ( /ˈæliːl/ or /əˈliːl/) is one of two or more forms of a gene or a genetic locus (generally a group of genes). The form "allel" is also used, an abbreviation of allelomorph. Sometimes, different alleles can result in different observable phenotypic traits, such as different pigmentation. However, many variations at the genetic level result in little or no observable variation.