Genetic drift

Definition

Genetic drift is a mechanism of evolution that refers to random changes in the allele frequencies of a population over time, particularly in small populations. It can lead to the loss of genetic variation and can cause alleles to become fixed or lost, impacting the overall genetic diversity of a species. This phenomenon is particularly important in understanding how populations evolve independently and can influence adaptation and speciation.

5 Must Know Facts For Your Next Test

1. Genetic drift has a more pronounced effect on small populations than on larger ones due to the limited number of individuals contributing to the gene pool.
2. Random events, such as natural disasters or disease outbreaks, can significantly influence allele frequencies through genetic drift.
3. Genetic drift can lead to fixation, where a particular allele becomes the only variant present in the population, resulting in reduced genetic diversity.
4. Unlike natural selection, which favors advantageous traits, genetic drift is entirely random and can result in either beneficial or detrimental changes to a population's genetic makeup.
5. Over time, genetic drift can contribute to speciation by causing populations to diverge genetically as they accumulate different alleles.

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 rather than consistent advantages conferred by specific traits. While natural selection promotes alleles that enhance survival and reproduction, genetic drift can lead to the loss or fixation of alleles purely by chance. This randomness means that genetic drift can result in both beneficial and harmful effects on a population's genetic structure without any regard for fitness.
• Discuss the implications of the bottleneck effect on genetic diversity within populations and how this relates to genetic drift.
  • The bottleneck effect occurs when a significant portion of a population is suddenly reduced, leading to a loss of genetic diversity. This reduction creates a situation where the remaining individuals' allele frequencies may not represent the original population's diversity, thereby magnifying the effects of genetic drift. As the population recovers, it may be left with limited variation and increased homozygosity, which can make it more vulnerable to environmental changes and reduce adaptability.
• Evaluate the role of genetic drift in speciation, particularly when considering the founder effect in isolated populations.
  • Genetic drift plays a crucial role in speciation by driving divergence among isolated populations. The founder effect illustrates how a small group establishing a new population can have drastically different allele frequencies compared to their source population due to random sampling of alleles. Over time, as these populations are subject to unique environmental pressures and continued genetic drift, they may accumulate enough differences in their gene pools that they become reproductively isolated from each other, ultimately leading to speciation.

Related terms

Bottleneck Effect: A sharp reduction in population size due to environmental events or human activities, leading to a loss of genetic diversity and altering allele frequencies.

Founder Effect: A form of genetic drift that occurs when a small group of individuals establishes a new population, resulting in a limited gene pool and 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, which can be affected by processes like genetic drift.