Genetic drift

Definition

Genetic drift is a mechanism of evolution that refers to random fluctuations in the frequency of alleles (gene variants) in a population over time. Unlike natural selection, which involves differential survival and reproduction, genetic drift occurs by chance and can lead to significant changes in the genetic makeup of small populations, potentially resulting in the loss of genetic diversity.

5 Must Know Facts For Your Next Test

1. Genetic drift is more pronounced in small populations because random events can have a larger impact on allele frequencies compared to larger populations.
2. This process can lead to the fixation or loss of alleles over generations, impacting the genetic diversity within a population.
3. Genetic drift can occur through mechanisms like random mating, environmental events, or migration patterns that inadvertently affect allele distribution.
4. While genetic drift is random, it can have significant evolutionary consequences, including the emergence of new species if populations diverge enough.
5. In some cases, genetic drift can counteract the effects of natural selection, causing beneficial alleles to become less common purely by chance.

Review Questions

• How does genetic drift differ from natural selection in terms of its impact on allele frequencies in a population?
  • Genetic drift differs from natural selection primarily in that it involves random fluctuations in allele frequencies rather than being driven by adaptive advantages. While natural selection favors alleles that enhance survival and reproduction, genetic drift can lead to changes regardless of an allele's effect on fitness. This means that alleles may increase or decrease in frequency simply due to chance events, especially in small populations where these random changes can have a larger impact.
• Discuss the implications of the bottleneck effect and founder effect as examples of how genetic drift can influence population genetics.
  • Both the bottleneck effect and founder effect serve as clear examples of how genetic drift can drastically alter allele frequencies within populations. The bottleneck effect occurs when a significant portion of a population is lost due to environmental events, leading to reduced genetic variation and potential loss of beneficial alleles. The founder effect arises when a small group starts a new population, limiting genetic diversity and causing the new population to reflect the alleles present in the founders. Both effects illustrate how chance events shape genetic structure over time.
• Evaluate the role of genetic drift in speciation processes and its long-term consequences for biodiversity.
  • Genetic drift plays a critical role in speciation processes by contributing to the divergence between isolated populations. As random changes accumulate over generations, populations may become genetically distinct enough that they can no longer interbreed even if they come back into contact. This isolation and differentiation can lead to the emergence of new species. In terms of long-term consequences for biodiversity, genetic drift can both enhance and reduce diversity; while it may contribute to the formation of new species, it can also lead to the loss of unique alleles and overall genetic variation within populations.

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 variation.

founder effect: A phenomenon that occurs when a small group of individuals establishes a new population, resulting in a limited genetic diversity that reflects the alleles of the founders.

allele frequency:

The proportion of a specific allele among all allele copies in a population, which can change over time due to mechanisms like genetic drift.