Dictionary > Allele


Reviewed by: Mary Anne Clark, PhD

Allele Definition
noun, plural: alleles

(genetics) Alleles are variants of a gene controlling the same trait and occupying a specific region on a chromosome (called the locus)

More Info

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.


What is a “gene”? What is an “allele”? Learn them in the context of a gene involved in PTC (phenylthiocarbamide) taste sensitivity. Credit: Amoeba Sisters




This worksheet is useful in helping the students assess their familiarity with the different parts of the cell, both the eukaryotic and the prokaryotic types. This is useful in genetics as it helps gauge the student’s knowledge of the difference between the two cell types, especially in terms of the location of the genetic material.

Subjects: Genetics & Evolution, Cell Biology
Lesson: Introduction to Genetics
Grades: 9th, 10th, 11th, 12th
Type: Worksheet

Word origin: From German Allel, shortened from Allelomorph, from English allelomorph


  • allelomorph

See also:

Related term(s):

Related form(s):

  • allelic (adjective, of, relating to, or pertaining to, an allele)
  • allelism (noun)
  • nonallelic (adjective, not functioning as alleles)

You will also like...