Genetic drift

Definition

Genetic drift is a mechanism of evolution that refers to random changes in allele frequencies within a population, particularly affecting small populations. This process can lead to significant evolutionary changes over time, especially when certain alleles become more or less common purely by chance, rather than through natural selection. It highlights how chance events can influence genetic variation and the evolutionary trajectory of a species.

5 Must Know Facts For Your Next Test

1. Genetic drift is more pronounced in small populations where random events can significantly impact allele frequencies.
2. One of the main outcomes of genetic drift is that it can lead to the fixation or loss of alleles in a population, drastically affecting its genetic diversity.
3. Unlike natural selection, genetic drift does not favor alleles that provide an advantage; changes occur randomly.
4. Genetic drift can result in populations becoming genetically distinct from one another, contributing to speciation over time.
5. The impact of genetic drift can be seen in isolated populations, such as island species, where their gene pool may diverge significantly from their mainland relatives.

Review Questions

• How does genetic drift differ from natural selection in terms of its impact on allele frequencies?
  • Genetic drift differs from natural selection in that it involves random changes in allele frequencies due to chance events rather than being influenced by an allele's fitness advantage. While natural selection results in the survival and reproduction of individuals with beneficial traits, genetic drift can lead to the random fixation or loss of alleles, regardless of whether they are advantageous or not. This randomness means that genetic drift can cause significant changes in small populations without regard to adaptation or survival.
• What are the implications of the bottleneck effect and founder effect for understanding genetic drift and its consequences for populations?
  • The bottleneck effect and founder effect illustrate how genetic drift can significantly alter the genetic makeup of populations. The bottleneck effect occurs when a population undergoes a drastic reduction in size due to environmental events, leading to a loss of genetic diversity and increased likelihood of inbreeding. The founder effect happens when a small group breaks away from a larger population to establish a new one, resulting in a limited gene pool. Both effects demonstrate how chance events can limit genetic variation and potentially lead to unique evolutionary pathways.
• Evaluate how genetic drift might contribute to speciation events among isolated populations over time.
  • Genetic drift can play a critical role in speciation, particularly among isolated populations. As random changes in allele frequencies accumulate over generations, populations may diverge genetically due to limited gene flow and distinct environmental pressures. These changes can result in reproductive isolation, as differing traits may arise that prevent interbreeding if individuals come into contact again. Over time, this divergence facilitated by genetic drift can solidify into distinct species, highlighting the importance of chance events in evolutionary processes.

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 phenomenon that occurs when a new population is established by a small number of individuals from a larger population, resulting in reduced genetic variation.

Allele Frequency: The proportion of a specific allele among all allele copies in a population, which can be influenced by genetic drift and other factors.