Genetic drift

Definition

Genetic drift is a mechanism of evolution that refers to random fluctuations in allele frequencies within a population from one generation to the next. This random process can lead to the loss of genetic variation, especially in small populations, and may cause certain alleles to become more or less common purely by chance rather than through natural selection. Understanding genetic drift is crucial for studying population genetics and the dynamics of allele frequencies in relation to Hardy-Weinberg equilibrium.

5 Must Know Facts For Your Next Test

1. Genetic drift has a more pronounced effect on small populations compared to large ones because random events can significantly alter allele frequencies.
2. Unlike natural selection, genetic drift is entirely random and does not necessarily favor advantageous traits, which can lead to maladaptive changes in populations.
3. The effects of genetic drift can lead to speciation, as isolated populations may diverge genetically over time due to random changes in allele frequencies.
4. Genetic drift can result in the fixation or loss of alleles, meaning that certain alleles may become the only variant present in a population or disappear entirely.
5. In the context of Hardy-Weinberg equilibrium, genetic drift violates the assumption of infinite population size, highlighting how real populations often experience fluctuations in allele frequencies.

Review Questions

• How does genetic drift differ from natural selection in terms of its impact on allele frequencies within a population?
  • Genetic drift differs from natural selection in that it operates through random chance rather than favoring alleles that confer a survival or reproductive advantage. While natural selection promotes the increase of beneficial traits based on environmental pressures, genetic drift can lead to random changes in allele frequencies regardless of their impact on fitness. This randomness means that genetic drift can cause both advantageous and disadvantageous alleles to fluctuate or even become fixed without any connection to their effects on survival.
• Discuss how the bottleneck effect serves as an example of genetic drift and its potential consequences for a population's genetic diversity.
  • The bottleneck effect occurs when a population undergoes a dramatic reduction in size due to environmental disasters or human actions, leading to a significant loss of genetic variation. As a result, the remaining individuals may not represent the full genetic diversity of the original population, causing certain alleles to become overrepresented or lost entirely. This loss of diversity can limit the population's ability to adapt to changing environments and increase its vulnerability to diseases, highlighting the detrimental consequences that genetic drift can have through mechanisms like the bottleneck effect.
• Evaluate the long-term implications of genetic drift on small populations and how this can affect evolutionary processes.
  • In small populations, genetic drift can have profound long-term implications by leading to reduced genetic diversity and increased fixation or loss of alleles over generations. These changes can affect evolutionary processes by hindering adaptive responses to environmental changes, as there may be fewer advantageous alleles available for selection. Additionally, if populations become isolated and experience different patterns of genetic drift, this divergence can ultimately lead to speciation. Therefore, understanding genetic drift is crucial for predicting evolutionary outcomes and maintaining biodiversity within ecosystems.

Related terms

bottleneck effect: A significant reduction in population size due to environmental events or human activities, which can lead to a loss of genetic diversity and changes in allele frequencies.

founder effect: A phenomenon that occurs when a small group of individuals establishes a new population, resulting in a limited gene pool and potentially different allele frequencies compared to the original population.

Hardy-Weinberg principle: A fundamental principle in population genetics that provides a mathematical framework for understanding allele frequencies in a population under ideal conditions, where no evolution occurs.