Genetic hitchhiking

Definition

Genetic hitchhiking is a phenomenon where an allele increases in frequency not because it is beneficial itself, but because it is located near a positively selected allele on the same chromosome. This occurs during the process of selection, as the advantageous allele causes nearby alleles to be carried along with it through generations, resulting in their increased frequency even if they provide no advantage. This effect can also lead to negative consequences when deleterious alleles are unintentionally swept along with beneficial ones.

5 Must Know Facts For Your Next Test

1. Genetic hitchhiking is most pronounced when there is strong positive selection for a nearby advantageous allele, which can cause rapid changes in allele frequencies.
2. This phenomenon can lead to the fixation of neutral or even harmful alleles due to their physical proximity to beneficial alleles on the same chromosome.
3. Genetic hitchhiking can reduce genetic variation within a population, as it may increase the frequency of linked alleles at the expense of others.
4. The concept is crucial for understanding how certain traits can spread through populations and influence overall genetic diversity.
5. It plays an important role in shaping genomic landscapes, especially in regions of low recombination where genes are closely linked.

Review Questions

• How does genetic hitchhiking illustrate the relationship between selection and allele frequencies in populations?
  • Genetic hitchhiking shows how the selection of one advantageous allele can inadvertently affect the frequency of nearby alleles. When a beneficial allele is positively selected, it often increases the likelihood that linked alleles will also rise in frequency, regardless of their individual effects. This demonstrates that selection can influence not only directly advantageous traits but also those that are merely associated with them, thus reshaping the genetic landscape of populations.
• Discuss the implications of genetic hitchhiking for understanding linkage disequilibrium within a population.
  • Genetic hitchhiking can create and maintain linkage disequilibrium, as it causes certain alleles to be inherited together more frequently than expected by chance. When a beneficial allele experiences positive selection, it pulls along nearby alleles, leading to increased associations between specific allele combinations. This can complicate interpretations of genetic data because the expected random assortment of alleles is disrupted, making it harder to identify true causal relationships in traits and diseases.
• Evaluate the potential long-term consequences of genetic hitchhiking on population genetics and evolutionary dynamics.
  • In the long run, genetic hitchhiking can lead to significant changes in population genetics by favoring certain alleles over others, even if they confer no benefit or are harmful. This may reduce genetic diversity within populations, making them less adaptable to environmental changes. Furthermore, it can influence evolutionary trajectories by promoting the spread of deleterious alleles alongside beneficial ones, which complicates our understanding of adaptation and survival. Overall, genetic hitchhiking shapes how populations evolve and respond to selective pressures over time.

Related terms

Linkage Disequilibrium: A condition in which alleles at different loci are associated more or less frequently than expected from random mating, often due to physical proximity on a chromosome.

Positive Selection:

The process through which beneficial mutations increase in frequency within a population, leading to adaptive traits becoming more common.

Genetic Drift: A mechanism of evolution that refers to random fluctuations in allele frequencies in a population, particularly in small populations.