Alleles


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Related to Alleles: genotype, Multiple alleles

Alleles

 

inherited imprints (genes) located in identical parts of homologous (paired) chromosomes; they determine the developmental direction of a particular characteristic. The term was introduced by the Danish scientist W. Johannsen in 1909 to replace the term “allelomorph,” which had been proposed by the English geneticist W. Bateson in 1902. Every gene may be found in at least two allelic states (determined by its structure), one of which—the dominant allele—usually assures maximal development of a given characteristic; the other—the recessive allele—leads to partial or complete loss of the characteristic. For example, in plants, the dominant allele produces colored flowers and the recessive allele produces colorless flowers; in humans, the gene controlling eye color is present in brown-eyed persons in the form of a dominant allele (either one or a pair), and in blue-eyed persons only in the form of recessive alleles. Genes belonging to a single allelic group are denoted by a single letter—uppercase for the dominant allele and lowercase for the recessive (for example, B and b). Only one allele of a given gene can be located in each homologous chromosome. Since there are two chromosomes of every type (homologous chromosomes) in diploid organisms, there are two alleles of every type in the somatic cells of such organisms. Only one allele, together with one of the chromosomes, appears in the formation of sex cells. During fertilization (fusion of sex cells) the parity of chromosomes, and hence also of alleles, is restored. Dominant and recessive alleles may be present in the state of homozygosity (BB or bb) or heterozygosity (Bb). If a gene is present in several (more than two) different states, it forms a series of multiple alleles.

REFERENCES

Lobashev, M. E. Genetika, 2nd ed. Leningrad, 1967.
Müntzing, A. Genetika. Moscow, 1967. (Translated from English.)

V. S. ANDREEV

References in periodicals archive ?
Because the chromosomes come in pairs, every dog has four alleles (gene codes) for color--one from the sire and one from the dam at both locus points.
Allele and genotype frequencies were calculated in patients by direct gene counting.
Another is that a tested alleged parent has copies of most, but not all of the child's alleles because he/she is a close relative of the true parent.
An analysis of data from three randomized trials studying the effects of genetic testing disclosure found that that cognitively healthy adults who learned that they were homozygous for the high-risk apolipoprotein E epsilon-4 allele (APOE epsilon-4) had a spike in test-specific distress score until about 6 months after learning the results but returned to levels similar to those of heterozygous carriers, reported Dr.
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In the present study, our aim was to determine the genotyping of the HLA- DRB1 alleles and certain HLA-DRB1 subgroups (HLA-DRB1*01, *04, *07, *08, *10) among the population in the Southeastern Anatolia Region of Turkey.
Other alleles of the ADH and ALDH genes also have been reported to affect risk; however, these effects are much smaller and are not detected in all studies.
It is possible that such common alleles/variants, like the RS3 allele in question, which are somehow involved in autism, will be associated with autistic-like traits such as being less communicative, more susceptible to anxiety and stress, and more self-oriented/introverted," Knafo said.
Many biology students struggle to understand key terms such as gene and allele even after classroom and laboratory instruction (Yilmaz et al.
5 per cent as compared to having no long alleles of the 5-HTT gene.