Allele

Definition

One of two or more variant forms of a gene or other DNA sequence occupying the same chromosomal locus. Alleles arise by mutation and are the basis of heritable genetic variation within populations.

Etymology

From German Allel, shortened from allelomorph (1902), coined by William Bateson from Greek allēl- 'one another' + morphē 'form'.

Example

In the mosquito Culex pipiens, the kdr (knockdown resistance) allele of the voltage-gated sodium channel gene confers resistance to pyrethroid insecticides; heterozygous individuals carrying one susceptible and one kdr allele show intermediate susceptibility.

Synonyms

• allelomorph

Related Terms

• locus
• Genotype
• phenotype
• heterozygosity
• homozygosity
• gene frequency
• single nucleotide polymorphism

Usage Notes

In diploid organisms, individuals carry two alleles per autosomal locus (one maternal, one paternal), which may be identical (homozygous) or different (heterozygous). In population genetics, allele frequencies describe the relative abundance of variants and change through selection, drift, mutation, or gene flow. The term applies broadly across eukaryotes, including haplodiploid Hymenoptera where males are hemizygous (single allele) at all loci.