Genetic drift

Definition

Genetic drift is a mechanism of evolution that refers to random changes in the frequency of alleles (gene variants) within a population over time. Unlike natural selection, which is driven by environmental pressures, genetic drift occurs due to chance events that can cause certain alleles to become more or less common, especially in small populations. This process can lead to significant genetic differences between populations, impacting their overall genetic diversity.

5 Must Know Facts For Your Next Test

1. Genetic drift can have a more pronounced effect in smaller populations, where random events can lead to larger shifts in allele frequencies.
2. It can lead to the fixation or loss of alleles in a population over time, influencing the genetic makeup of future generations.
3. Unlike natural selection, genetic drift does not necessarily favor alleles that are beneficial for survival and reproduction.
4. Genetic drift can contribute to speciation by causing populations to diverge genetically when they become isolated from each other.
5. Random mating within a population does not prevent genetic drift; it can still occur regardless of how individuals mate.

Review Questions

• How does genetic drift differ from natural selection in terms of its effects on allele frequencies within a population?
  • Genetic drift differs from natural selection in that it operates through random chance rather than through environmental pressures that favor certain traits. While natural selection increases the frequency of advantageous alleles that enhance survival and reproduction, genetic drift can randomly increase or decrease allele frequencies regardless of their impact on fitness. This randomness means that under genetic drift, beneficial alleles can be lost while harmful ones may become more common purely by chance.
• Discuss how the bottleneck effect can influence genetic diversity and the long-term evolutionary trajectory of a population.
  • The bottleneck effect occurs when a significant reduction in population size leads to a loss of genetic diversity. This reduction limits the variety of alleles available for future generations, potentially reducing the population's ability to adapt to environmental changes. Over time, this lack of diversity can make populations more vulnerable to diseases and reduce their overall fitness, steering their evolutionary path in unexpected directions compared to populations that maintained higher levels of genetic variation.
• Evaluate the role of genetic drift in speciation events and its implications for understanding evolutionary processes.
  • Genetic drift plays a crucial role in speciation by driving divergence between populations over time, especially when they become geographically isolated. As different populations experience random changes in allele frequencies due to genetic drift, they may accumulate distinct genetic characteristics. If these differences become substantial enough, they can lead to reproductive isolation, resulting in the emergence of new species. Understanding this process highlights how chance events contribute to biodiversity and illustrates that evolution is not solely guided by natural selection but also involves unpredictable factors.

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 and altering allele frequencies.

Founder effect: A phenomenon where a small group of individuals establishes a new population, leading to a limited gene pool and potentially different allele frequencies compared to the original population.

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