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Definition

noun, plural: alleles

(genetics)

One member of a pair (or any of the series) of genes occupying a specific spot on a chromosome (called locus) that controls the same trait.

Supplement

For example, a pair of alleles controlling the same trait, i.e. eye color: one allele codes for blue eyes, another allele for brown eyes.

In humans, simple traits such as eye color may be caused by the interaction of only one pair of alleles. But for complex traits, such as height, they are usually caused by the interactions of series of alleles. Some alleles are dominant over other alleles, as in the case of heterozygous pairings (where paired alleles are different, in contrast to homozygous pairings where alleles are the same). In the above example, since the alleles code for different eye colors they are heterozygous.

Colloquially, the term gene is used when referring to an inherited trait that is usually accompanied by a phenotype as in ‘tall genes’ or ‘bad genes’ – but the more proper (scientific) term for this is allele.

Word origin: From German Allel, shortened from Allelomorph, from English allelomorph.
Related forms: allelic (adjective), biallelic (adjective), diallelic (adjective), monoallelic (adjective), allelism (noun), nonallelic (adjective).
Synonym: allelomorph.
See also: gene, trait, loci, DNA, chromosome.