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Related Concept Videos

Frequency-dependent Selection01:21

Frequency-dependent Selection

When the fitness of a trait is influenced by how common it is (i.e., its frequency) relative to different traits within a population, this is referred to as frequency-dependent selection. Frequency-dependent selection may occur between species or within a single species. This type of selection can either be positive—with more common phenotypes having higher fitness—or negative, with rarer phenotypes conferring increased fitness.Positive Frequency-Dependent SelectionIn positive...
Malaria01:29

Malaria

Malaria pathogenesis in humans reflects a delicate interplay between parasite biology and host response. Clinical illness reflects a host’s immune response to the parasite’s asexual replication cycle, which is often asymptomatic in individuals with partial immunity. From the parasite's perspective, transmission between mosquito and human with minimal host pathology is evolutionarily advantageous. Among the six Plasmodium species infecting humans, P. falciparum and P. vivax dominate in global...
Hardy-Weinberg Principle01:49

Hardy-Weinberg Principle

Diploid organisms have two alleles of each gene, one from each parent, in their somatic cells. Therefore, each individual contributes two alleles to the gene pool of the population. The gene pool of a population is the sum of every allele of all genes within that population and has some degree of variation. Genetic variation is typically expressed as a relative frequency, which is the percentage of the total population that has a given allele, genotype or phenotype.In the early 20th century,...
Mutation, Gene Flow, and Genetic Drift01:09

Mutation, Gene Flow, and Genetic Drift

In a population that is not at Hardy-Weinberg equilibrium, the frequency of alleles changes over time. Therefore, any deviations from the five conditions of Hardy-Weinberg equilibrium can alter the genetic variation of a given population. Conditions that change the genetic variability of a population include mutations, natural selection, non-random mating, gene flow, and genetic drift (small population size).Mechanisms of Genetic VariationThe original sources of genetic variation are mutations,...
Types of Selection01:46

Types of Selection

Natural selection influences the frequencies of particular alleles and phenotypes within populations in several different ways. Primarily, natural selection can be directional, stabilizing, or disruptive. Directional selection favors one extreme trait and shifts the population towards that phenotype while selecting against individuals displaying alternate traits. Stabilizing selection favors an intermediate trait with a narrow range of variation. Deviation from the optimal phenotype towards an...
Mismatch Repair01:20

Mismatch Repair

Organisms are capable of detecting and fixing nucleotide mismatches that occur during DNA replication. This sophisticated process requires identifying the new strand and replacing the erroneous bases with correct nucleotides. Mismatch repair is coordinated by many proteins in both prokaryotes and eukaryotes.
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The human genome has more than 3 billion base pairs of DNA per cell. Prior to cell division, that vast amount of genetic...

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MHC allele frequency distributions under parasite-driven selection: A simulation model.

Maciej Jan Ejsmond1, Wiesław Babik, Jacek Radwan

  • 1Institute of Environmental Sciences, Jagiellonian University, ul, Gronostajowa 7, 30-387 Kraków, Poland. maciek.ejsmond@uj.edu.pl

BMC Evolutionary Biology
|October 29, 2010
PubMed
Summary

The Ewens-Watterson test effectively detects balancing selection on Major Histocompatibility Complex (MHC) genes due to heterozygote advantage. However, it struggles to detect selection when negative frequency-dependent selection is involved.

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Area of Science:

  • Evolutionary genetics
  • Immunogenetics
  • Population genetics

Background:

  • Major Histocompatibility Complex (MHC) genes exhibit extreme polymorphism, potentially driven by parasite-mediated selection.
  • Two key mechanisms proposed are heterozygote advantage and negative frequency-dependent selection.
  • The Ewens-Watterson (EW) test assesses selection by comparing observed allele frequencies to neutral expectations.

Purpose of the Study:

  • To investigate the utility of the EW test in detecting selection on MHC genes.
  • To evaluate EW test performance under heterozygote advantage and negative frequency-dependent selection, both individually and combined.
  • To understand how parasite-driven selection impacts MHC genetic diversity detection.

Main Methods:

  • Utilized computer simulations to model selection pressures on MHC genes.
  • Simulated conditions included heterozygote advantage and negative frequency-dependent selection.
  • Analyzed allele frequency distributions generated by simulations using the EW test.

Main Results:

  • Heterozygote advantage alone resulted in more even allele frequencies, detectable by the EW test.
  • Negative frequency-dependent selection, alone or combined with heterozygote advantage, yielded unpredictable allele frequency distributions.
  • Most simulations under negative frequency-dependent selection showed distributions indistinguishable from neutral expectations.

Conclusions:

  • The EW test has limited utility for detecting selection on MHC genes when negative frequency-dependent selection is a significant factor.
  • Relying solely on the EW test may underestimate the role of negative frequency-dependent selection in maintaining MHC diversity.
  • Further development of statistical methods is needed to accurately detect selection under complex evolutionary pressures.