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Related Concept Videos

Epistasis01:39

Epistasis

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In addition to multiple alleles at the same locus influencing traits, numerous genes or alleles at different locations may interact and influence phenotypes in a phenomenon called epistasis. For example, rabbit fur can be black or brown depending on whether the animal is homozygous dominant or heterozygous at a TYRP1 locus. However, if the rabbit is also homozygous recessive at a locus on the tyrosinase gene (TYR), it will have an unshaded coat that appears white, regardless of its TYRP1...
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Epistasis Analysis01:09

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Although Mendel chose seven unrelated traits in peas to study gene segregation, most traits involve multiple gene interactions that create a spectrum of phenotypes. When the interaction of various genes or alleles at different locations influences a phenotype, this is called epistasis. Epistasis often involves one gene masking or interfering with the expression of another (antagonistic epistasis). Epistasis often occurs when different genes are part of the same biochemical pathway. The...
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Limits to Natural Selection01:38

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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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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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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.
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Mutagenesis and Functional Selection Protocols for Directed Evolution of Proteins in E. coli
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How does epistasis influence the response to selection?

N H Barton1

  • 1Institute of Science and Technology Austria, Klosterneuburg, Austria.

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|December 1, 2016
PubMed
Summary
This summary is machine-generated.

The infinitesimal model in quantitative genetics assumes weak selection on many genes. This model holds even with gene interactions, suggesting selection efficiently accumulates information in this regime.

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Area of Science:

  • Quantitative genetics
  • Population genetics
  • Evolutionary genetics

Background:

  • The infinitesimal model is foundational in quantitative genetics, assuming negligible selection on genetic variance.
  • This model is often justified by a large number of loci with additive effects, but also applies with gene interactions if selection is weak relative to drift.

Purpose of the Study:

  • To explore the validity and implications of the infinitesimal model in quantitative genetics.
  • To investigate the role of epistasis and selection strength in adaptation and trait optimization.

Main Methods:

  • Theoretical analysis of genetic models under selection and drift.
  • Review of empirical evidence on selection strength and allele effects.

Main Results:

  • The infinitesimal model remains relevant even with epistasis, provided the number of loci is large.
  • Stabilizing selection can maintain traits near optima, but is limited by drift load (~4Ne), which can be overcome by negative epistasis.
  • Selection accumulates information most efficiently in the infinitesimal regime where allele selection is weak and comparable to drift.

Conclusions:

  • The infinitesimal model provides a robust framework for understanding adaptation, particularly when selection on individual alleles is weak.
  • Substantial adaptation can occur through alleles operating within the infinitesimal regime, where epistasis has moderate effects.