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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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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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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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Determining epistatic selection in admixed populations.

Molly Schumer1,2, Yaniv Brandvain3

  • 1Department of Ecology and Evolutionary Biology, Princeton University, Princeton, NJ, 08544, USA.

Molecular Ecology
|April 11, 2016
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Summary
This summary is machine-generated.

Researchers developed ancestry disequilibrium (AD) scans to detect genetic incompatibilities between diverging species. While demographic factors can bias results, the study shows AD scans can identify genuine incompatibilities in admixed populations.

Keywords:
ancestry disequilibriumepistasishybrid incompatibilitieshybridizationlinkage disequilibrium

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Area of Science:

  • Evolutionary genetics
  • Speciation research
  • Population genetics

Background:

  • Hybridization between diverging species can be limited by genetic incompatibilities.
  • Ancestry disequilibrium (AD) scans examine nonrandom ancestry associations at unlinked loci in admixed populations to identify incompatibilities.
  • Previous studies reported excess positive AD, suggesting widespread incompatibilities.

Purpose of the Study:

  • To investigate biases in ancestry disequilibrium (AD) scans caused by demographic factors.
  • To develop methods for accurately interpreting AD scan results in the context of species divergence.
  • To identify candidate genetic incompatibilities in natural hybridizing populations.

Main Methods:

  • Forward simulations to model demographic effects on AD.
  • Development of a novel AD measure to reduce bias.
  • Reanalysis of existing data from admixed Xiphophorus fish populations.

Main Results:

  • Realistic demographic scenarios, including recent hybridization, can create a bias towards positive AD.
  • A novel AD measure partially mitigates, but does not eliminate, this bias.
  • The extreme tail of the AD distribution is enriched for true incompatibilities.
  • Co-enrichment of top AD hits in Xiphophorus populations supports the utility of AD scans.

Conclusions:

  • The prevalence of positive AD alone does not confirm widespread two-locus incompatibilities.
  • AD scans, when interpreted cautiously, can identify candidate interspecific incompatibilities.
  • Further methodological refinement is needed to fully disentangle demographic effects from true genetic incompatibilities.