allele(n = noun.body) allelomorph - (genetics) either of a pair (or series) of alternative forms of a gene that can occupy the same locus on a particular chromosome and that control the same character; "some alleles are dominant over others"
one of two or more alternative forms of a gene that can have the same place on homologous chromosomes and are responsible for alternative traits. [WordNet 1.5]
either of a pair of Mendelian characters that may occur in an organism as a consequence of variation at one gene locus. [PJC]