Genetic drift

Definition

Genetic drift is a mechanism of evolution that refers to random changes in allele frequencies within a population, which can lead to significant genetic variation over time. This process occurs more noticeably in small populations, where chance events can result in certain alleles becoming more or less common, independent of natural selection. Genetic drift can have profound implications for molecular evolution and the estimation of divergence times between species.

5 Must Know Facts For Your Next Test

1. Genetic drift can cause alleles to become fixed (reach 100% frequency) or lost (reach 0% frequency) in a population purely by chance.
2. It is particularly impactful in small populations where random events can lead to greater fluctuations in allele frequencies compared to larger populations.
3. Genetic drift can lead to speciation by causing isolated populations to diverge genetically over time.
4. Unlike natural selection, genetic drift does not favor any particular trait; changes in allele frequencies are completely random.
5. Studies using molecular data often consider the effects of genetic drift when estimating divergence times between species, as it influences genetic similarities and differences.

Review Questions

• How does genetic drift differ from natural selection in terms of its impact on allele frequencies?
  • Genetic drift differs from natural selection primarily in that it is a random process rather than a selective one. While natural selection favors alleles that provide a reproductive advantage, leading to their increase in frequency, genetic drift can cause any allele to fluctuate in frequency without regard to its impact on survival or reproduction. This randomness can lead to significant changes in small populations, whereas larger populations may experience less pronounced effects from genetic drift.
• Discuss how the bottleneck effect and founder effect are examples of genetic drift and their implications for genetic diversity.
  • Both the bottleneck effect and founder effect are significant examples of genetic drift that illustrate how population size can influence genetic diversity. The bottleneck effect occurs when a large population experiences a drastic reduction in size, leading to a loss of genetic diversity as only a small number of individuals contribute to the gene pool. Similarly, the founder effect takes place when a new population is established by a small group from a larger population, resulting in reduced genetic variation. Both effects highlight how random events can dramatically alter allele frequencies and reduce overall genetic diversity.
• Evaluate the role of genetic drift in understanding molecular evolution and divergence time estimation among species.
  • Genetic drift plays a critical role in molecular evolution by influencing the patterns of genetic variation within and between populations. It can complicate the interpretation of molecular data when estimating divergence times among species because it introduces randomness that may obscure relationships dictated by natural selection. When researchers analyze molecular sequences, accounting for the effects of genetic drift helps clarify how closely related species are and provides insights into their evolutionary histories. Understanding these dynamics allows for more accurate models and predictions regarding the timing of speciation events.

Related terms

bottleneck effect: A sharp reduction in the size of a population due to environmental events or human activities, leading to a loss of genetic diversity.

founder effect: A reduction in genetic diversity that occurs when a small group of individuals becomes isolated from a larger population and establishes a new population.

allele frequency: The relative frequency of an allele at a genetic locus in a population, often expressed as a proportion or percentage.