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Demographic changes, like population size shifts, can mimic genetic diversity reductions caused by selective sweeps. This study quantitatively compares "neutral sweeps" from population changes to actual selective sweeps, revealing subtle differences in their genetic diversity patterns.

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Area of Science:

  • Population Genetics
  • Evolutionary Biology
  • Genomics

Background:

  • Reduced genetic diversity around a locus often indicates a selective sweep, driven by positive selection.
  • However, demographic events like population size changes can also cause similar reductions in diversity, complicating interpretation.
  • Distinguishing between demographic effects and selective sweeps is crucial for understanding evolutionary processes.

Purpose of the Study:

  • To quantitatively investigate the shape of diversity valleys resulting from demographic changes (neutral sweeps).
  • To compare these neutral sweeps with the patterns generated by selective sweeps.
  • To provide insights into differentiating demographic influences from positive selection in genetic variation data.

Main Methods:

  • Developed and analyzed a simple population genetics model incorporating a single population size change.
  • Derived analytical descriptions for the expected shape of diversity valleys under neutral demographic scenarios.
  • Compared the quantitative characteristics (e.g., width) of these neutral valleys to those produced by selective sweeps.

Main Results:

  • Selective sweep valleys of genetic diversity are analytically shown to be wider than neutral valleys for the same fixation time.
  • It is possible to parameterize the neutral model to generate valleys with the same width as a given selected valley.
  • Demographic processes can indeed create patterns of nucleotide diversity that are highly similar to those resulting from positive selection.

Conclusions:

  • Simple demographic models, particularly population size changes, can generate genetic diversity patterns resembling selective sweeps.
  • While differences in valley width exist, they may not always be sufficient for unambiguous distinction.
  • These findings highlight the significant role of demography in shaping observed patterns of genetic variation and necessitate careful consideration when inferring selection.