allele


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Related to allele: Dominant allele, multiple allele, Recessive 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 ?
In another study, the COMBINE trial, which found a "robust" effect of treatment with naltrexone over placebo among those with the Asp40 allele, "naltrexone seemed to be moderated by the presence of the Asp40 allele," with "essentially no effect" of naltrex one in the homozygous (Asn40/Asn40) group, he noted (Arch.
To enable this resource to grow, users have the opportunity to opt-in to join the Allele Frequency Community and benefit from the extensive database, agreeing in return to contribute statistics from their sequences to the database.
Samples carrying an expanded allele showed broader melt profiles that dropped to baseline -dF/dT levels at or above 87[degrees]C.
Conversely, 26 per cent of those with the short-short allele were dissatisfied, compared to only 20 per cent of those with the long-long variant.
Allele frequencies were determined for 12 polymorphisms in nine genes in the folate-MTX metabolic pathway in 144 healthy subjects.
A real-time polymerase chain reaction assay for quantification of allele ratios and correction of amplification bias.
Prediction did not improve substantially when ST or clonal complex information was added to allele information.
Thus, the presence of the ADH1C*2 allele would be associated with a slightly reduced oxidizing capacity, whereas the presence of ADH1B*2 and ADH1B*3 alleles would be associated with a substantially higher oxidative capacity (i.
Noble, MD, PhD, a former director of the National Institute on Alcohol Abuse and Alcoholism (NIAAA) who has conducted significant research on the A1 allele of the D2 dopamine receptor gene, believes further knowledge about the A1 allele could lead to the development of dopamine agonists that would act in the same way as alcohol and other abused substances.
1 Given each parent's genetic makeup, assign an uppercase letter for a dominant allele (one that expresses a visible trait) and a lowercase letter for a recessive allele (one that is masked by a dominant trait).
Because each allele appears to be independently associated with type 2 diabetes, it is thought that each one has a unique role in diabetes, development.