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Related Concept Videos

Types of Selection01:46

Types of Selection

37.5K
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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Limits to Natural Selection01:38

Limits to Natural Selection

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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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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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Mutation, Gene Flow, and Genetic Drift01:09

Mutation, Gene Flow, and Genetic Drift

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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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Genetic Variation01:25

Genetic Variation

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Genetic variation is the diversity in DNA sequences found among individuals of the same species. This diversity is crucial for a species' survival because it helps organisms adapt to environmental changes. Genetic variation begins with fertilization, where an egg and sperm cell merge. Each of these cells carries 23 chromosomes, up to 46 in the fertilized egg. Chromosomes are long DNA strands that contain genes, the basic units of heredity.
Genes exist in different versions called alleles,...
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Hardy-Weinberg Principle01:49

Hardy-Weinberg Principle

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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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Following the Dynamics of Structural Variants in Experimentally Evolved Populations
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Simulation of genetic systems : XI. Normalizing selection.

R Allen1, A Fraser

  • 1Department of Animal Husbandry, University of California, Davis.

TAG. Theoretical and Applied Genetics. Theoretische Und Angewandte Genetik
|January 21, 2014
PubMed
Summary
This summary is machine-generated.

Intense normalizing selection effectively reduces heterozygosity, but its impact diminishes with more loci. Tight linkage initially speeds up heterozygosity loss but becomes less significant as the number of loci increases.

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Area of Science:

  • Population genetics
  • Evolutionary biology
  • Quantitative genetics

Background:

  • Normalizing selection is a key evolutionary force.
  • Understanding selection's impact on genetic diversity is crucial.
  • Previous studies have explored selection on few loci.

Purpose of the Study:

  • To investigate the impact of intense normalizing selection on heterozygosity.
  • To examine how the number of loci affects selection's effectiveness.
  • To assess the role of linkage in modulating selection's effects.

Main Methods:

  • Computer simulations were employed.
  • Models with varying numbers of loci (3 to 24) were analyzed.
  • The influence of free recombination versus tight linkage was simulated.

Main Results:

  • Selection's effectiveness in reducing heterozygosity decreases as the number of loci increases.
  • With free recombination, selection's impact approaches that of random genetic drift at many loci.
  • Tight linkage initially enhances heterozygosity loss but this effect diminishes with more loci.

Conclusions:

  • Normalizing selection is less potent in reducing heterozygosity across numerous loci.
  • Linkage plays a complex role, with its influence waning as locus number grows.
  • These findings have implications for understanding genetic diversity maintenance in evolving populations.