Allelism

any of several forms of a gene, usually arising through mutation, that are responsible for hereditary variation.
noun
any of two or more variants of a gene that have the same relative position on homologous chromosomes and are responsible for alternative characteristics, such as smooth or wrinkled seeds in peas Also called allelomorph (əˈliːləˌmɔːf) See also multiple alleles
n.

1931, from German allel, abbreviation of allelomorph (1902), coined from Greek allel- “one another” (from allos “other;” see alias) + morphe “form” (see Morpheus).

allele al·lele (ə-lēl’)
n.
One member of a pair or series of genes that occupies a specific position on a specific chromosome. Also called allelomorph.
al·le’lic (ə-lē’lĭk, ə-lěl’ĭk) adj.
allele
(ə-lēl’)
Any of the possible forms in which a gene for a specific trait can occur. In almost all animal cells, two alleles for each gene are inherited, one from each parent. Paired alleles (one on each of two paired chromosomes) that are the same are called homozygous, and those that are different are called heterozygous. In heterozygous pairings, one allele is usually dominant, and the other recessive. Complex traits such as height and longevity are usually caused by the interactions of numerous pairs of alleles, while simple traits such as eye color may be caused by just one pair.
allele [(ul-leel)]

The sequence of nucleotides on a DNA molecule that constitutes the form of a gene at a specific spot or a chromosome. There can be several variations of this sequence, and each of these is called an allele. In the case of the gene for eye color, for example, one allele codes for blue eyes, whereas the other may code for brown eyes.