An allele (short for allelomorph) is a variant of a gene were the DNA sequence differs between two or more variants. Allelic variation describes the presence or number of different allele forms at a particular locus (locus or loci = place) on a chromosome (allelic variation is sometimes used more loosely to describe the overall diversity present). During domestication the number of alleles that are fixed within a crop type is greatly reduced compared to the variation that is left behind in the genepool. Therefore there may be many unadapted useful allelic variants that could be used to improve our domesticated crop types.