Balancing selection

Definition

Balancing selection is a type of natural selection that maintains genetic diversity within a population by favoring the presence of multiple alleles at a given gene locus. This process ensures that no single allele becomes fixed or dominant, allowing for various traits to coexist and providing the population with a greater adaptive potential to changing environments. The importance of balancing selection can be seen in its role in maintaining health and fitness within modern human populations, where different genetic variants can offer protection against various diseases.

5 Must Know Facts For Your Next Test

1. Balancing selection can occur through mechanisms like heterozygote advantage, where individuals carrying two different alleles have increased survival or reproductive success.
2. It plays a crucial role in maintaining the genetic diversity of populations, particularly in response to environmental pressures such as disease and climate change.
3. Certain diseases, like malaria, have shown how balancing selection can favor the sickle cell allele in regions where malaria is prevalent, providing resistance to the disease.
4. In human populations, balancing selection has contributed to diverse immune responses, which can enhance survival against pathogens.
5. The concept of balancing selection highlights the importance of genetic variability for the adaptability and resilience of modern human populations.

Review Questions

• How does balancing selection influence genetic diversity in modern human populations?
  • Balancing selection influences genetic diversity by favoring multiple alleles at specific gene loci, which allows for a wider range of traits to exist within a population. This increased genetic variation provides a buffer against environmental changes and diseases, enabling some individuals to survive and reproduce despite varying conditions. As a result, balancing selection contributes to the overall health and adaptability of modern human populations.
• Discuss the role of heterozygote advantage in balancing selection and provide an example from human genetics.
  • Heterozygote advantage is central to balancing selection as it promotes the coexistence of different alleles within a population. An example of this is seen in regions where malaria is endemic, where individuals who are heterozygous for the sickle cell trait (carrying one normal hemoglobin allele and one sickle cell allele) have a survival advantage over those with normal hemoglobin or sickle cell disease. This advantage results in higher frequencies of the sickle cell allele in these populations due to balancing selection.
• Evaluate the implications of balancing selection on the evolution of human populations in response to changing environmental pressures.
  • The implications of balancing selection on human evolution are significant, as it fosters genetic diversity that enhances adaptability to changing environments. As humans face new challenges such as emerging diseases and climate shifts, balancing selection ensures that various genetic variants can provide different advantages under different conditions. This dynamic process contributes not only to individual health outcomes but also shapes population-level responses to environmental pressures, making understanding this mechanism crucial for predicting future evolutionary trajectories and health risks in human populations.

Related terms

allele: A variant form of a gene that arises by mutation and is found at the same place on a chromosome.

heterozygote advantage: A situation where individuals with two different alleles for a specific gene have a higher fitness than those with two identical alleles.

genetic drift: A mechanism of evolution that refers to random changes in the frequency of alleles in a population, which can lead to reduced genetic variation.