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MHC class I proteins form a functional receptor on most nucleated cells of the body. [1] There are three major and three minor MHC class I genes in HLA. Major MHC class I HLA-A; HLA-B; HLA-C; Minor genes are HLA-E, HLA-F and HLA-G. β 2-microglobulin binds with major and minor gene subunits to produce a heterodimer.
Among all those genes present in MHC, there are two types of genes coding for the proteins MHC class I molecules and MHC class II molecules that are directly involved in the antigen presentation. These genes are highly polymorphic, 19031 alleles of class I HLA, and 7183 of class II HLA are deposited for human in the IMGT database. [16]
The MHC class I genes originated in the most recent common ancestor of all jawed vertebrates, and have been found in all living jawed vertebrates that have been studied thus far. [2] Since their emergence in jawed vertebrates, this gene family has been subjected to many divergent evolutionary paths as speciation events have taken place.
If the genes of a gene family encode proteins, the term protein family is often used in an analogous manner to gene family. The expansion or contraction of gene families along a specific lineage can be due to chance, or can be the result of natural selection. [2] To distinguish between these two cases is often difficult in practice.
The Atlantic salmon, Salmo salar, is one species in which sperm competition is influenced by the variation in the major histocompatibility complex, specifically that of the Class I alleles. Atlantic salmon males have higher rates of successful fertilization when competing for eggs from females genetically similar at the class I genes of the MHC ...
Gene conversion is the process by which one DNA sequence replaces a homologous sequence such that the sequences become identical after the conversion. [1] Gene conversion can be either allelic, meaning that one allele of the same gene replaces another allele, or ectopic, meaning that one paralogous DNA sequence converts another.
A null allele is a gene variant that lacks the gene's normal function because it either is not expressed, or the expressed protein is inactive. For example, at the gene locus for the ABO blood type carbohydrate antigens in humans, [13] classical genetics recognizes three alleles, I A, I B, and i, which determine compatibility of blood transfusions.
When a locus is identified as imprinted, two different classes express different alleles. [65] Inherited imprinted genes of offspring are believed to be monoallelic expressions. A single locus will entirely produce one's phenotype although two alleles are inherited. This genotype class is called parental imprinting, as well as dominant ...