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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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Incomplete Dominance01:43

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Gregor Mendel's work (1822 - 1884) was primarily focused on pea plants. Through his initial experiments, he determined that every gene in a diploid cell has two variants called alleles inherited from each parent. He suggested that amongst these two alleles, one allele is dominant in character and the other recessive. The combination of alleles determines the phenotype of a gene in an organism.
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Frequency-dependent Selection01:21

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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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Although the genetic makeup of an organism plays a major role in determining the phenotype, there are also several environmental factors, such as temperature, oxygen availability, presence of mutagens, that can alter an organism’s phenotype.
An example of how genetic background affects phenotype can be seen in horses. The Extension gene in horses is responsible for their coat color. A wild-type gene (EE) produces black pigment in the coat, while a mutant gene (ee) produces red pigment. A...
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Law of Independent Assortment02:03

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While Mendel’s Law of Segregation states that the two alleles for one gene are separated into different gametes, a different question of how different genes are inherited remains. For example, is the gene for tall plants inherited with the gene for green peas? Mendel asked this question by experimenting with a dihybrid cross; a cross in which both parents are homozygous for two distinct traits resulting in an F1 generation that are heterozygous for both traits.
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Resolving the Conflict Between Associative Overdominance and Background Selection.

Lei Zhao1, Brian Charlesworth2

  • 1Centre for Computational Systems Biology, Fudan University, Shanghai 200433, People's Republic of China.

Genetics
|May 17, 2016
PubMed
Summary

Genetic drift impacts neutral loci variability. In small populations, selection can slow variability loss, while in large populations, background selection accelerates it, affecting genetic diversity.

Keywords:
associative overdominancebackground selectiondeleterious mutationsheterozygote advantageneutral variability

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Area of Science:

  • Population Genetics
  • Evolutionary Biology
  • Molecular Evolution

Background:

  • Genetic linkage can influence variability at neutral loci.
  • Background selection in large populations reduces neutral variability.
  • Associative overdominance can occur in small populations.

Purpose of the Study:

  • To investigate conditions influencing variability loss at neutral loci linked to selected loci.
  • To differentiate between variability retardation and acceleration.
  • To understand the interplay of population size, selection, and mutation.

Main Methods:

  • Analytical studies
  • Numerical simulations
  • Population genetics modeling

Main Results:

  • Variability loss is retarded only when S (effective population size * selection coefficient) is of order 1.
  • Background selection accelerates variability loss when S >> 1.
  • Apparent heterozygote advantage at neutral loci is observed with partially recessive mutations.
  • Heterozygote advantage at selected loci nearly always retards variability loss.

Conclusions:

  • Population size and selection strength critically determine variability dynamics at linked neutral loci.
  • Understanding these dynamics is crucial for interpreting experimental data and simulation results.
  • The findings have implications for studying genetic diversity in various populations.