Words similar to overdominance
Example sentences for: overdominance
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Moreover, direct estimates of the allele-specific effects of heterozygosity (relative to the corresponding homozygotes), nearly absent in the infectious disease-HLA literature, are frequently found in studies of HLA genotype and chronic (mostly autoimmune) diseases [ 28 29 30 ] . We do not know the reason for this difference in approach, but suspect that some infectious disease investigators, informed by the evolutionary hypothesis of overdominance for infectious disease resistance and by animal studies, may have a special interest in detecting effects of heterozygosity per se . Many studies of HLA-autoimmune disease associations, on the other hand, seem to focus more on the effects of individual alleles and, having established these, move on to investigate the dependence of these effects on genetic modifiers, including the identity of the individual's other allele at the same locus.
From the perspective of the population genetics debate concerning the role of overdominance in maintaining polymorphism at the MHC, we should note that this mechanism requires allele-specific overdominance for total fitness, not for resistance to individual diseases.
Because these studies group all homozygotes and group all heterozygotes, they do not, in fact, test the hypothesis of allele-specific overdominance, which is conditional on the alleles involved.
We have shown that when allele-specific overdominance exists, it will often be manifest as population heterozygote advantage, but that a finding of population heterozygote advantage may be consistent with other patterns of allele-specific effects; for example, when resistant and susceptible alleles are equally common and equally diverse, population heterozygote advantage will occur if allele-specific effects are additive, dominant or overdominant.
As an alternative to directly examining the hypothesis of allele-specific overdominance, several investigators have compared the infectious disease outcomes of heterozygotes at a given HLA locus, as a group, to the outcomes of homozygotes at the same locus, as a group.
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