allele

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Related to Allelle: multiple allele, Recessive allele, Dominant allele

allele

(əlēl`): see geneticsgenetics,
scientific study of the mechanism of heredity. While Gregor Mendel first presented his findings on the statistical laws governing the transmission of certain traits from generation to generation in 1856, it was not until the discovery and detailed study of the
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.

Allele

Any of a number of alternative forms of a gene. Allele is a contraction of allelomorph, a term used to designate one of the alternative forms of a unit showing mendelian segregation. New alleles arise from existing ones by mutation. The diversity of alleles produced in this way is the basis for hereditary variation and evolution. The different alleles of a given gene determine the degree to which the specific hereditary characteristic controlled by that gene is manifested. The particular allele which causes that characteristic to be expressed in a normal fashion is often referred to as the wild-type allele. Mutations of the wild-type allele result in mutant alleles, whose functioning in the development of the organism is generally impaired relative to that of the wild-type allele. See Deoxyribonucleic acid (DNA), Gene, Gene action, Genetic code, Mendelism, Mutation

An allele occupies a fixed position or locus in the chromosome. In the body cells of most higher organisms, including humans, there are two chromosomes of each kind and hence two alleles of each kind of gene, except for the sex chromosomes. Such organisms and their somatic cells are said to carry a diploid complement of alleles. A diploid individual is homozygous if the same allele is present twice, or heterozygous if two different alleles are present. Let A and a represent a pair of alleles of a given gene; then A/A and a/a are the genetic constitutions or genotypes of the two possible homozygotes, while A/a is the genotype of the heterozygote. Usually the appearance or phenotype of the A/a individuals resembles that of the A/A type; A is then said to be the dominant allele and a the recessive allele. In the case of the sex chromosomes, one sex (usually the male in most higher animals, with the exception of birds) has only one X chromosome, and the Y lacks almost all of the genes in X. The male thus carries only one dose of X-linked genes and is said to be hemizygous for alleles carried on his X chromosome. As a result, if a male inherits a recessive mutant allele such as color blindness on his X chromosome, he expresses color blindness because he lacks the wild-type allele on his Y chromosome. See Chromosome, Sex-linked inheritance

In a population of diploid individuals, it is possible to have more than two alleles of a given gene. The aggregate of such alleles is called a multiple allelic series. Since genes are linear sequences of hundreds or even thousands of nucleotide base pairs, the potential number of alleles of a given gene which can arise by base substitution alone is enormous.

allele

[ə′lēl]
(genetics)
One of the alternate forms of a gene at a gene locus on a chromosome. Also known as allelomorph.

allele

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
References in periodicals archive ?
When using fluorescence probes for specific loci on allelles, a homozygous locus has greater intensity on the allele that is present.