Genetic drift: random changes in allele frequencies
Genetic drift is the random fluctuation of allele frequencies in populations, reducing genetic variation over time—especially in small or isolated populations—and distinct from natural selection.
Overview
Genetic drift is the change in the frequency of genetic variants (alleles) in a population caused by random sampling effects from one generation to the next. Unlike natural selection, which is directional and depends on fitness differences, drift operates by chance: some alleles become more common or are lost simply because their carriers leave more descendants by accident. Its impact is strongest in small or isolated populations, where chance events can substantially shift allele frequencies over a few generations. For further context see introductory resources.
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Mechanisms and consequences
Key outcomes of genetic drift include loss of genetic variation, random fixation of alleles, and divergence between separated populations. Two commonly discussed phenomena are the bottleneck effect, where a population is sharply reduced and survivors carry only a subset of the original variation, and the founder effect, where a new population starts from a small number of individuals and reflects their alleles by chance. These mechanisms change the genetic structure of populations and can influence traits indirectly even when alleles have no effect on fitness. Read more at explanatory pages.
Distinction from natural selection
Genetic drift is nondirectional and blind to adaptive value: neutral or even deleterious alleles can increase in frequency through drift. Natural selection, by contrast, systematically increases the frequency of alleles that improve reproductive success. In real populations both processes act together; the relative importance depends largely on population size and the strength of selection. See a comparison overview at comparative discussion.
History and theoretical development
The concept grew from early 20th-century population genetics and became part of the neutral theory of molecular evolution, which proposes that many molecular changes are due to random drift of selectively neutral mutations. Theoretical work introduced the idea of effective population size, a key parameter that quantifies how strongly drift affects a population compared with an idealized model. Additional reading is available via historical notes.
Importance and applications
Genetic drift matters in conservation biology (small endangered populations lose diversity), in understanding founder effects during colonization, and in interpreting molecular variation between species. Empirical studies use genetic markers to monitor allele-frequency changes and to distinguish drift from selection. Practical guidance and case studies can be found at applied resources.
Questions and answers
Q: What is genetic drift?
A: Genetic drift is a random effect on biological populations which reduces the amount of genetic variation in the population.
Q: What are some forces that add heritable variation to a population?
A: Mutation and recombination are two forces which add heritable variation to a population.
Q: Are there any factors that remove variation from a population?
A: Yes, genetic drift is one factor which removes variation from a population.
Q: How does genetic drift reduce the amount of genetic variation in a population?
A: Genetic drift reduces the amount of genetic variation in a population by randomly removing certain alleles or gene variants from the gene pool over time.
Q: Is mutation an example of something that adds heritable variation to a population?
A: Yes, mutation is an example of something that adds heritable variation to a population.
Q: What other force can add heritable variations to populations besides mutation and recombination?
A: There are no other known forces besides mutation and recombination which can add heritable variations to populations.
Sources
- evolution.berkeley.edu : Evolution 101:Sampling Error and Evolution
- evolution.berkeley.edu : Effects of Genetic Drift
- evolution.berkeley.edu : Evolution 101: Peripatric Speciation
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AlegsaOnline.com Genetic drift: random changes in allele frequencies Leandro Alegsa
URL: https://en.alegsaonline.com/art/37993