Drift: Theoretical Aspects

Abstract

Drift is the process by which gene frequency changes erratically in a population. Random sampling of gametes at reproduction is the main cause of drift, and therefore the population size of a species is most important, that is often measured by the effective size. Homozygosity and inbreeding may increase by drift. The significance of drift has become clear in studies of population genetics and evolution at the molecular level by the expansion of genome data. The effects of drift are estimated by statistical analyses of molecular data on polymorphisms and divergence among related species. In particular, the interplay of drift and selection is most important in understanding the evolution of interaction systems at various levels. Epigenetic mechanisms have significant influences on the interplay. Drift, selection, environmental factors, and epigenetics are thought to work together here.

Key Concepts:

  • Random sampling of gametes at reproduction is the major cause of drift in a finite population.

  • Interplay of drift and selection is essential for evolution of complex systems, and the two become inseparable.

  • Robust genetic systems enhance the effects of drift.

  • Epigenetics gives opportunities for drift and selection to respond to environmental changes.

Keywords: stochastic process; selective neutrality and near‐neutrality; effective population size; interplay of drift and selection; evolution of complex systems

Figure 1.

Illustration of the process of random sampling of gametes at reproduction. An idealised case of four individuals is shown. Reproduced with permission from Kimura, .

Figure 2.

A few sample paths representing changes of gene frequency by drift in six identical populations (N=10), starting from 0.5. Reproduced with permission from Kimura, .

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References

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Further Reading

Akashi H (1995) Inferring weak selection from patterns of polymorphism and divergence at ‘silent’ sites in Drosophila DNA. Genetics 139: 1067–1076.

Bell O, Tiwar VK, Thoma NH and Schubeler D (2011) Determinants and dynamics of genome accessibility. Nature 12: 554–564. www.nature.com/reviews/genetics.

Bird A (2010) DNA methylation patterns and epigenetic memory. Genes & Development 16: 6–21. Doi: 10.1101/gad.947102.

Cohen NM, Kenisberg E and Tanay A (2011) Primate CpG islands are maintained by heterogeneous evolutionary regimes involving minimal selection. Cell 145: 773–786. DOI 10.1016/j.cell2011.04.024.

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Hartl DL and Clark AG (2007) Principles of Population Genetics, Fourth edn. Sunderland, MA: Sinauer Associates.

Li W‐H (1997) Molecular Evolution. Sunderland, MA: Sinauer Associates.

Sawyer S, Parsch J, Zhang Z and Hartl DL (2007) Prevalence of positive selection among nearly neutral amino acid replacements in Drosophila. Proceedings of the National Academy of Sciences of the USA 104: 6504–6510. www.pnas.org/cgi/doi/10.1073/pnas.0701572104.

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How to Cite close
Ohta, Tomoko(Jun 2012) Drift: Theoretical Aspects. In: eLS. John Wiley & Sons Ltd, Chichester. http://www.els.net [doi: 10.1002/9780470015902.a0001772.pub3]