Genetic drift

Definition

Genetic drift is a mechanism of evolution that refers to random changes in allele frequencies within a population over time, often due to chance events. This process can lead to significant shifts in genetic variation, particularly in small populations, where the effects of random sampling are more pronounced. Genetic drift contrasts with natural selection, as it does not favor traits that provide a survival or reproductive advantage but rather leads to changes that are incidental and stochastic.

5 Must Know Facts For Your Next Test

1. Genetic drift is especially impactful in small populations where random events can lead to larger changes in allele frequencies compared to larger populations.
2. The two major effects of genetic drift are the bottleneck effect and the founder effect, both of which can significantly alter genetic diversity.
3. Unlike natural selection, genetic drift does not lead to adaptations; instead, it can cause beneficial or harmful alleles to become more or less common purely by chance.
4. Over time, genetic drift can lead to speciation, as isolated populations may diverge genetically due to random changes and loss of variation.
5. Genetic drift is an important concept in conservation biology, as understanding its effects can help manage small or endangered populations.

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 its mechanism and outcomes. While natural selection promotes the survival and reproduction of individuals with advantageous traits, thereby increasing the frequency of those alleles over time, genetic drift operates randomly and without regard for the fitness of alleles. This randomness means that alleles can increase or decrease in frequency purely by chance events, especially in small populations where the effects are magnified.
• Discuss how the bottleneck effect can lead to reduced genetic diversity in a population and provide an example.
  • The bottleneck effect occurs when a population experiences a significant reduction in size due to events such as natural disasters or human activities. This drastic reduction leads to a loss of genetic variation because only a small number of individuals contribute to the gene pool afterward. For example, the northern elephant seal faced severe hunting in the 19th century, reducing its population to just about 20 individuals. As a result, the genetic diversity was drastically reduced, making them more susceptible to diseases and environmental changes.
• Evaluate the role of genetic drift in speciation and how it may influence evolutionary pathways.
  • Genetic drift plays a critical role in speciation by promoting divergence among isolated populations. As populations become separated geographically or reproductively, random changes in allele frequencies can lead to significant genetic differences over time. This divergence can affect traits related to mating, survival, or adaptation to local environments, ultimately resulting in new species formation. Such processes illustrate how evolutionary pathways are influenced not just by adaptive traits through natural selection but also by stochastic events that shape genetic variation and population dynamics.

Related terms

allele frequency: The relative frequency of an allele (variant of a gene) at a genetic locus in a population, which can change due to mechanisms like genetic drift.

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

founder effect: A form of genetic drift that occurs when a small group of individuals becomes isolated from a larger population, leading to a reduction in genetic variation and potentially different allele frequencies.