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 ?
Study of frequency of alleles showed that major allele (M) for SNP rs2802288 in our local population is "G", while the minor allele (m) is "A".
Allele frequency is to display gene diversity in one population of one species.
H = 1 - IPSPi2 where, H is genetic diversity index and Pi is frequency of the number of alleles at the locus.
HLA-C alleles have been associated with protection against AIDS development, particularly for patients exhibiting the -35C allele upstream of the HLA-C gene, which has been reported to be associated with high cellular expression of HLA-C molecules and protection against HIV [7, 8].
Conclusions: Data demonstrates that frequency and distribution of mutant T allele was more prevalent as compared to wild type A allele in the study group.
In unselected Mestizos from the greater Valley of Mexico region, the frequency of theHLA-DRB1 alleles with risk for MS is: HLA-DRB1*15 in 5.5-10.5%; HLA-DRB1*08 in 7.8-16.2%; and HLA-DRB1*04 in 1.5-4.5% (22).
At the American Heart Association Meeting in 2015, it was announced that the protective FOXO3 allele is strongly associated with reduced coronary heart disease mortality (p=0.00001) (AHA Meeting 2015) and later published in the leading gerontology journal (Willcox et al.
However, there was no significant difference between the controls and the UC patients in the three FUT2 mutant alleles or genotype frequencies (all P > 0.05).
Allele frequencies were estimated by the gene counting method, and the chi-square test was used to identify significant departures from the Hardy-Weinberg equilibrium.
Sequence variability across HLA genes was quantified by calculating the Shannon entropy (23, 24) at each position of the multiple sequence alignment (MSA) of HLA-A, HLA-B, and HLA-C alleles respectively.
The HLA molecules present antigenic peptides to T lymphocyte and modulate the host-tumor immune response.[sup][6] Except for NPC, HLA polymorphism has a role in malignant diseases such as breast cancer,[sup][7] hepatocellular carcinoma,[sup][8] lymphoma,[sup][9] and cervical cancer.[sup][10] Different HLA -Class I alleles have been reported to be associated with NPC in Southern China.