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Related Concept Videos

Types of Selection01:46

Types of Selection

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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...
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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.
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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.
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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).
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Organisms that are well-adapted to their environment are more likely to survive and reproduce. However, natural selection does not lead to perfectly adapted organisms. Several factors constrain natural selection.
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Evolutionary dynamics in the two-locus two-allele model with weak selection.

Martin Pontz1,2, Josef Hofbauer3, Reinhard Bürger3

  • 1Institut für Mathematik, Universität Wien, Oskar-Morgenstern-Platz 1, 1090, Wien, Austria. martin.pontz@univie.ac.at.

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|May 27, 2017
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Summary
This summary is machine-generated.

This study simplifies population genetics models by ignoring linkage disequilibrium under weak selection. It characterizes evolutionary dynamics and equilibrium structures for various epistasis models, offering insights into polymorphism maintenance.

Keywords:
EpistasisEquilibrium structureLinkage disequilibriumPhase portraitRecombinationSelection

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Area of Science:

  • Population Genetics
  • Evolutionary Biology
  • Mathematical Biology

Background:

  • Two-locus, two-allele models are foundational in population genetics for studying epistasis.
  • Epistasis's complexity, particularly linkage disequilibrium, has hindered general insights.
  • Previous models often struggle with mathematical complexity.

Purpose of the Study:

  • To characterize all possible equilibrium structures and evolutionary flows in two-locus models under weak selection.
  • To simplify analysis by assuming linkage disequilibrium can be ignored.
  • To provide a general framework for understanding epistasis's role in evolutionary problems.

Main Methods:

  • Mathematical modeling of population genetics dynamics.
  • Analysis of equilibrium structures and phase portraits.
  • Application of index theory to infer polymorphic equilibria from marginal dynamics.
  • Approximation of weak selection relative to recombination.

Main Results:

  • Complete characterizations of equilibrium structures for specific fitness schemes (additive, additive-by-additive epistasis, haploid, multilinear, marginal over/underdominance, symmetric viability).
  • Inference of polymorphic equilibria number and stability from boundary flows.
  • Demonstration of epistasis's influence on boundary flows and internal equilibrium structures.

Conclusions:

  • Ignoring linkage disequilibrium under weak selection provides a tractable approach to studying epistasis.
  • The analysis offers a comprehensive understanding of evolutionary dynamics for various genetic models.
  • Index theory is a powerful tool for analyzing complex population genetic systems.