Genetic drift

Definition

Genetic drift is a mechanism of evolution that refers to random changes in the frequency of alleles (gene variants) in a population over time. It occurs due to chance events that lead to some alleles being passed on to the next generation more frequently than others, independent of natural selection. This randomness can significantly affect small populations, leading to reduced genetic variation and potential fixation or loss of alleles.

5 Must Know Facts For Your Next Test

1. Genetic drift can lead to random changes in allele frequencies, especially in small populations where chance events have a more significant impact.
2. It can result in the fixation of harmful alleles, which may decrease the overall fitness of the population over time.
3. Unlike natural selection, genetic drift does not favor alleles that provide any advantage; it is purely a random process.
4. As populations become isolated or fragmented, genetic drift can cause divergence between populations, contributing to speciation.
5. Over many generations, genetic drift can lead to the loss of genetic diversity, making populations more vulnerable to environmental changes.

Review Questions

• How does genetic drift differ from natural selection in terms of its impact on allele frequencies?
  • Genetic drift differs from natural selection primarily because it operates randomly rather than through selective pressures. While natural selection favors traits that enhance survival and reproduction, leading to an increase in advantageous alleles, genetic drift can randomly cause certain alleles to become more or less common regardless of their effects on fitness. This randomness can lead to significant shifts in allele frequencies over generations, especially in small populations.
• Discuss the implications of the bottleneck effect on genetic diversity within a population and how this relates to genetic drift.
  • The bottleneck effect occurs when a population's size is drastically reduced due to an event like a natural disaster or human activity. This leads to a sharp reduction in genetic diversity as only a small number of individuals contribute genes to the next generation. This situation exemplifies genetic drift because the random survival of certain alleles can significantly alter allele frequencies and limit the population's ability to adapt to future environmental changes. The decreased genetic variation can also make the population more susceptible to diseases and other pressures.
• Evaluate how the founder effect illustrates the principles of genetic drift and its potential consequences for newly established populations.
  • The founder effect is a clear example of genetic drift where a small group establishes a new population away from the original one. This situation can lead to reduced genetic variation because the new population's gene pool is limited to the alleles present in the founders. As a result, certain traits may become overrepresented while others are lost entirely. This lack of diversity can have profound implications, as it may hinder the new population's ability to adapt to changing environments and increase their risk of extinction if they encounter adverse conditions.

Related terms

bottleneck effect: A phenomenon where a significant reduction in population size results in a loss of genetic diversity and alters allele frequencies due to random sampling of the surviving population.

founder effect: A type of genetic drift that occurs when a small group from a larger population establishes a new population, potentially carrying only a small fraction of the genetic variation present in the original group.

allele frequency: The relative frequency of an allele (variant of a gene) in a population, usually expressed as a proportion or percentage.