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.

either of a pair of Mendelian characters that may occur in an organism as a consequence of variation at one gene locus.

Any one of two or more genes occupying the same location on a chromosome, determining a given trait (such as eye color, production of a particular enzyme, etc.).

An alternative form of a given gene. For each gene there are two alleles, one on each chromosome of a chromosome pair. One allele is inherited from the mother, the other from the father.