A shorthand form of allelomorph, one of a series of possible alternative forms of a given gene, differing in DNA sequence, and affecting the functioning of a single product (RNA and/or protein) (King et al. 2006). Any of the forms of the same gene that occur at the same locus on a homologous chromosome but differ in base sequence (Oxford 2006). One of several alternate forms of a gene occupying a given locus on a chromosome or plasmid (Viljoen et al. 2005). One of two or more alternative forms of a gene at a particular locus. If more than two alleles exist, the locus is said to exhibit multiple allelism (Hoy 2003). Form of a gene. Genes are considered allelic when they occur in the same position on members of a chromosome pair (Resh and Cardé 2003). Mutually exclusive form of the same gene, occupying the same locus on homologous chromosomes, and governing the same biochemical and developmental process (NAL 2008). See ‘gene’.