Genetic drift

Definition

Genetic drift is the random change in the frequency of alleles (gene variants) in a population due to chance events. This process can lead to significant changes in a population's genetic makeup over time, especially in small populations, where random events can have a more pronounced effect. It contrasts with natural selection, which involves differential survival and reproduction based on advantageous traits.

5 Must Know Facts For Your Next Test

1. Genetic drift can result in the loss of genetic variation within small populations, making them more vulnerable to extinction.
2. It is particularly influential in isolated populations, where random events can significantly alter allele frequencies over generations.
3. Unlike natural selection, genetic drift does not necessarily favor beneficial traits; it is purely random and can lead to harmful alleles becoming more common.
4. The effects of genetic drift are more pronounced in smaller populations due to their limited gene pool.
5. Genetic drift can contribute to speciation by causing populations to diverge genetically when isolated over time.

Review Questions

• How does genetic drift differ from natural selection in terms of its impact on allele frequencies within populations?
  • Genetic drift differs from natural selection as it involves random changes in allele frequencies rather than changes based on advantageous traits. While natural selection promotes traits that enhance survival and reproduction, genetic drift can lead to the increase or decrease of alleles regardless of their adaptive value. This means that harmful or neutral alleles may become more common in a population due to chance events, illustrating how random processes can influence evolutionary outcomes.
• Discuss the significance of the founder effect and bottleneck effect as examples of genetic drift and their implications for genetic diversity.
  • The founder effect and bottleneck effect are both examples of genetic drift that illustrate how population size and history can impact genetic diversity. The founder effect occurs when a small group establishes a new population, leading to reduced genetic variation as only a subset of alleles is represented. The bottleneck effect arises when a significant portion of a population is suddenly reduced, often resulting in decreased genetic diversity due to the limited number of survivors. Both effects highlight how random events can drastically affect the genetic health and adaptability of populations.
• Evaluate how genetic drift can play a role in speciation events and what factors might enhance this process over time.
  • Genetic drift can contribute to speciation by creating distinct genetic differences between isolated populations. As populations diverge due to random allele frequency changes over generations, they may accumulate enough differences that they become reproductively isolated from one another. Factors that enhance this process include geographic isolation, environmental pressures unique to each population, and limited gene flow. These conditions allow genetic drift to operate more effectively, leading to greater divergence and the potential emergence of new species over time.

Related terms

Bottleneck Effect: A sharp reduction in the size of a population due to environmental events or human activities, leading to decreased genetic diversity.

Founder Effect: The reduced genetic diversity that occurs when a small group from a larger population establishes a new population, carrying only a fraction of the original population's genetic variation.

Allele Frequency: The relative frequency of an allele at a genetic locus in a population, expressed as a proportion of the total number of alleles for that gene.