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Frequency-dependent Selection01:21

Frequency-dependent Selection

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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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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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Natural selection—probably the most well-known evolutionary mechanism—increases the prevalence of traits that enhance survival and reproduction. However, evolution does not merely propagate favorable traits, nor does it always benefit populations.
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Physiological and compartmental models are valuable tools used in studying biological systems. These models rely on differential equations to maintain mass balance within the system, ensuring an accurate representation of the dynamic processes at play.
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A goodness-of-fit test is conducted to determine whether the observed frequency values are statistically similar to the frequencies expected for the dataset. Suppose the expected frequencies for a dataset are equal such as when predicting the frequency of any number appearing when casting a die. In that case, the expected frequency is the ratio of the total number of observations (n)  to the number of categories (k).
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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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Fluctuating Selection in the Moran.

Antony M Dean1,2,3, Clarence Lehman2, Xiao Yi2,3

  • 1State Key Laboratory of Biocontrol, School of Life Sciences, Sun Yat-sen University, Guangzhou 510275, People's Republic of China deanx024@umn.edu.

Genetics
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Summary
This summary is machine-generated.

Fluctuating selection, contrary to classical theory, can maintain genetic diversity (polymorphism) in populations. This dynamic process also accelerates evolution and impacts genetic divergence patterns.

Keywords:
Moran modelfluctuating selectionheterozygosityrate of evolution

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Area of Science:

  • Evolutionary Biology
  • Population Genetics
  • Molecular Evolution

Background:

  • Classical population genetics theory often assumes constant selection pressures.
  • Previous models did not fully account for the impact of fluctuating selection on genetic diversity.
  • Understanding factors that maintain genetic polymorphism is crucial for evolutionary studies.

Purpose of the Study:

  • To investigate the effect of fluctuating selection on haploid polymorphism.
  • To determine how fluctuating selection influences heterozygosity and fixation probabilities.
  • To compare the impact of fluctuating selection on polymorphism versus divergence.

Main Methods:

  • Analytical derivations based on the Moran model.
  • Forward simulations using the Moran model.
  • Mathematical modeling extending the classical neutral model.

Main Results:

  • Fluctuating selection with a mean selection coefficient of zero promotes polymorphism, contrary to classical theory.
  • Increased heterozygosity is observed with rapid fluctuations, weak mutation, large population size, and high selection variance.
  • Fluctuating selection increases dN/dS ratios for both polymorphism and divergence, with a more pronounced effect on divergence.

Conclusions:

  • Randomly fluctuating selection is a significant factor in maintaining genetic diversity and driving evolutionary rates.
  • The model provides a parsimonious explanation for diverse evolutionary observations, including patterns seen in comparative genomics.
  • Fluctuating selection increases the probability of allele fixation, particularly under strong selection and weak mutation.