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, especially in small populations. This process can lead to significant changes in the genetic makeup of a population due to chance events, rather than natural selection. It plays a crucial role in shaping genetic diversity and can impact evolutionary pathways, influencing everything from human origins to the broader principles of Darwinian evolution.

5 Must Know Facts For Your Next Test

1. Genetic drift is more pronounced in small populations, where random events can have a larger impact on allele frequencies.
2. Unlike natural selection, which favors traits that improve survival and reproduction, genetic drift can lead to the loss of beneficial traits simply by chance.
3. The founder effect is a specific type of genetic drift that occurs when a new population is established by a small number of individuals, leading to reduced genetic variation.
4. The bottleneck effect often results from catastrophic events, such as natural disasters, which drastically reduce population size and alter genetic diversity.
5. Over time, genetic drift can result in populations diverging genetically, even if they originate from the same ancestral group.

Review Questions

• How does genetic drift differ from natural selection in terms of its impact on allele frequencies in a population?
  • Genetic drift differs from natural selection primarily in that it is a random process, whereas natural selection is driven by environmental pressures favoring advantageous traits. In genetic drift, allele frequencies can change by chance alone, particularly in small populations where random events can have outsized effects. This randomness can lead to the loss or fixation of alleles without regard for their potential benefits to survival or reproduction.
• Evaluate the significance of the bottleneck and founder effects in understanding the implications of genetic drift on human origins.
  • The bottleneck and founder effects are critical for understanding how genetic drift has shaped human origins. The bottleneck effect illustrates how dramatic reductions in population size can result in significant losses of genetic diversity, which can impact the long-term adaptability of humans. Similarly, the founder effect highlights how small groups migrating to new areas can carry limited genetic variation, potentially influencing the genetic structure of future populations. Both effects demonstrate how chance events have played substantial roles in human evolutionary history.
• Synthesize how genetic drift, alongside natural selection and gene flow, contributes to the overall process of evolution within species.
  • Genetic drift, natural selection, and gene flow together create a complex picture of evolution within species. While natural selection promotes adaptive changes based on environmental pressures, genetic drift introduces randomness that can lead to significant shifts in allele frequencies over generations. Gene flow facilitates the exchange of genes between populations, introducing new alleles and enhancing genetic diversity. Together, these mechanisms ensure that populations evolve dynamically, with genetic drift playing a key role in maintaining variation and influencing evolutionary trajectories.

Related terms

Allele Frequency: The proportion of a specific allele among all alleles for a particular gene in a population.

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

Founder Effect: A phenomenon that occurs when a small group of individuals establishes a new population, which may carry only a small fraction of the genetic diversity of the original population.