Genetic Hitchhiking

Definition

Genetic hitchhiking refers to the phenomenon where an allele increases in frequency in a population because it is located near a beneficial allele that is being favored by natural selection. This occurs when the advantageous allele enhances the survival or reproductive success of individuals carrying it, causing neighboring alleles on the same chromosome to also be carried along, even if they are neutral or deleterious. This process illustrates the link between genetic variation and population genetics, as it highlights how selection can affect not just specific traits but entire segments of the genome.

5 Must Know Facts For Your Next Test

1. Genetic hitchhiking occurs when a neutral or harmful allele increases in frequency due to its physical proximity to a beneficial allele that is under positive selection.
2. This phenomenon can lead to reduced genetic diversity in regions of the genome surrounding the selected allele, as linked alleles may also be fixed or lost together.
3. Genetic hitchhiking can be observed in various species and has been documented in human populations where certain alleles are associated with advantageous traits like disease resistance.
4. The strength of genetic hitchhiking depends on factors like the selection coefficient of the beneficial allele and the recombination rate between loci.
5. Understanding genetic hitchhiking helps researchers infer past selection events in populations by examining patterns of linkage disequilibrium and allele frequencies.

Review Questions

• How does genetic hitchhiking illustrate the relationship between natural selection and genetic variation within a population?
  • Genetic hitchhiking showcases how natural selection can affect not just individual alleles that confer advantages, but also neighboring alleles that are physically linked on chromosomes. When a beneficial allele increases in frequency due to its positive impact on fitness, it carries along adjacent alleles, leading to changes in genetic variation across the population. This interconnectedness highlights the complexity of evolutionary processes where selection impacts entire genomic regions rather than isolated genes.
• What role does linkage disequilibrium play in understanding the effects of genetic hitchhiking on population genetics?
  • Linkage disequilibrium arises when certain alleles at different loci are associated more often than expected by chance, which can be a direct consequence of genetic hitchhiking. When a beneficial allele is favored by natural selection, its linked alleles may also increase in frequency due to their proximity on the chromosome. By analyzing patterns of linkage disequilibrium, scientists can gain insights into historical selection pressures and how they shaped current genetic diversity within populations.
• Evaluate how genetic drift and natural selection interact with genetic hitchhiking to shape evolutionary outcomes in populations.
  • Genetic drift and natural selection can interact in complex ways with genetic hitchhiking. While natural selection promotes the spread of beneficial alleles, genetic drift introduces randomness that can affect allele frequencies regardless of their fitness. In small populations, drift might overpower selection, potentially leading to fixation of neutral or even harmful alleles through hitchhiking. Conversely, strong selective pressures can amplify hitchhiking effects, reducing overall genetic diversity and influencing evolutionary trajectories. Understanding this interaction helps clarify how populations evolve over time under varying environmental conditions.

Related terms

Linkage Disequilibrium: A non-random association of alleles at different loci in a given population, often resulting from genetic hitchhiking or other evolutionary forces.

Selective Sweep: The process where a beneficial allele increases in frequency and sweeps through a population, reducing genetic diversity at nearby loci due to genetic hitchhiking.

Genetic Drift: A mechanism of evolution that involves random fluctuations in allele frequencies in a population, which can impact the effects of genetic hitchhiking.