Explain how selection, the founder effect and genetic drift, including the bottleneck effect, may affect allele frequencies in populations

SouravNovember 1, 2024

Answered step-by-step

Natural selection, the founder effect, and genetic drift (including the bottleneck effect) are key mechanisms that influence allele frequencies within populations. Each of these processes operates under different conditions and has distinct effects on genetic variation.

Natural Selection

Natural selection is the process by which individuals with advantageous traits are more likely to survive and reproduce, leading to changes in allele frequencies over time. This mechanism relies on several conditions:

1. Variation: There must be variation in traits within a population.
2. Heritability: Traits must be heritable, allowing them to be passed from parents to offspring.
3. Differential Survival and Reproduction: Individuals with traits that confer a survival advantage are more likely to reproduce, thereby increasing the frequency of those advantageous alleles in subsequent generations.

For example, if a particular allele enhances an organism’s ability to find food or evade predators, individuals carrying that allele will have higher reproductive success, leading to an increase in its frequency in the population over time

Founder Effect

The founder effect occurs when a small group of individuals breaks away from a larger population to establish a new population. This small founding group may not represent the genetic diversity of the original population, resulting in reduced genetic variation and altered allele frequencies.

• Mechanism: When the new population is established by a limited number of founders, certain alleles may be overrepresented or underrepresented purely by chance. This can lead to significant differences between the new population and the original one.
• Example: The Afrikaner population in South Africa is known for having a high frequency of certain genetic disorders, such as Huntington’s disease, due to the small number of Dutch settlers who founded it. Many of these founders carried specific alleles at higher frequencies than would be expected in a larger, more genetically diverse population

Genetic Drift

Genetic drift refers to random changes in allele frequencies that occur in small populations due to chance events. It can lead to significant shifts in genetic variation over time and is particularly pronounced during events like population bottlenecks.

Bottleneck Effect

The bottleneck effect is a specific type of genetic drift that occurs when a significant portion of a population is suddenly reduced due to an event (e.g., natural disaster, disease). The surviving individuals may have different allele frequencies compared to the original population.

• Mechanism: After a bottleneck event, the reduced population may lack genetic diversity because only a small number of alleles are represented among the survivors. This can hinder the population’s ability to adapt to environmental changes.
• Example: Northern elephant seals experienced a severe bottleneck due to extensive hunting in the 19th century, reducing their numbers to about 20 individuals. Although their population has rebounded, they now exhibit significantly lower genetic diversity compared to populations that were not subjected to such drastic reductions

Conclusion

In summary, natural selection drives changes in allele frequencies based on adaptive advantages, while the founder effect and genetic drift introduce random fluctuations that can lead to reduced genetic diversity and altered allele distributions within populations. Understanding these mechanisms is crucial for comprehending how populations evolve over time and how they may respond to environmental pressures.

References

1. Biology LibreTexts. (n.d.). Genetic Drift. Retrieved from https://bio.libretexts.org/Bookshelves/Introductory_and_General_Biology/Map:_Raven_Biology_12th_Edition/20:_Genes_Within_Populations/20.09:_Interactions_Among_Evolutionary_Forces/20.9.2:_Genetic_Drift
2. Wikipedia. (2024). Founder effect. Retrieved from https://en.wikipedia.org/wiki/Founder_effect
3. Understanding Evolution. (n.d.). Bottlenecks and founder effects. Retrieved from https://evolution.berkeley.edu/bottlenecks-and-founder-effects/
4. National Human Genome Research Institute. (2024). Founder Effect. Retrieved from https://www.genome.gov/genetics-glossary/Founder-Effect
5. Nature Education Scitable. (n.d.). Natural Selection, Genetic Drift, and Gene Flow Do Not Act in Isolation in Evolutionary Processes. Retrieved from https://www.nature.com/scitable/knowledge/library/natural-selection-genetic-drift-and-gene-flow-15186648
6. Nature Education Scitable. (n.d.). Evolutionary Adaptation and Positive Selection in Humans. Retrieved from https://www.nature.com/scitable/topicpage/evolutionary-adaptation-in-the-human-lineage-12397