noun, plural: alleles
Alleles are variants of a gene controlling the same trait, encoding a version of the same product (usually a protein), and occupying a specific region on a chromosome. That region is called a locus. In eukaryotes, in which two parents may contribute either the same or different alleles to their progeny, the alleles come in pairs. An example of alleles is seen in the flower color of garden peas: one allele produces purple flowers and another produces white flowers. In individuals that have two different alleles (heterozygous) the trait encoded by one of the two alleles may be preferentially expressed and is called dominant. The unexpressed allele is called recessive and is expressed only when it is the only allele present (homozygous). In peas, the allele for purple color is dominant to the allele for white color.
Although alleles are identified as different versions of the same gene, for some genes only a single allele is known. For others, e.g. the beta globins, there may be hundreds of alleles identified, with variable effects on the phenotype.
In humans, many traits, e.g. eye color and height, are determined by the interaction of alleles at multiple loci. These are called polygenic traits.
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
- allelic (adjective, of, relating to, or pertaining to, an allele)
- allelism (noun)
- nonallelic (adjective, not functioning as alleles)