Balancing selection

Definition

Balancing selection is a type of natural selection that maintains genetic diversity in a population by favoring the survival of multiple alleles, rather than just the dominant or the most advantageous allele. This process often occurs in heterogeneous environments where different alleles confer advantages under varying conditions. It can lead to the preservation of genetic variations that might otherwise be lost, resulting in a stable equilibrium of allele frequencies over time.

5 Must Know Facts For Your Next Test

1. Balancing selection helps maintain genetic variation by allowing multiple alleles to persist within a population, which can be critical for adaptability to changing environments.
2. This type of selection is often observed in cases where different alleles confer advantages against diseases or environmental stresses, like the sickle cell trait providing resistance to malaria.
3. Balancing selection can occur through mechanisms such as heterozygote advantage and negative frequency-dependent selection, each promoting diversity in different ways.
4. The preservation of multiple alleles can lead to stable populations that are better equipped to handle fluctuations in their environment, promoting long-term survival.
5. In contrast to directional selection, which favors one allele over others, balancing selection maintains an equilibrium where no single allele becomes fixed.

Review Questions

• How does balancing selection contribute to the maintenance of genetic diversity within populations?
  • Balancing selection contributes to genetic diversity by favoring the survival of multiple alleles within a population, preventing any single allele from becoming dominant. This is especially important in environments that fluctuate or vary, as different alleles may offer advantages under different conditions. As a result, balancing selection promotes a more varied gene pool, which can enhance a population's ability to adapt and survive over time.
• Discuss the mechanisms by which balancing selection operates, particularly focusing on heterozygote advantage and negative frequency-dependent selection.
  • Balancing selection operates through several mechanisms, including heterozygote advantage and negative frequency-dependent selection. Heterozygote advantage occurs when individuals with two different alleles at a locus have higher fitness than those who are homozygous. Negative frequency-dependent selection allows rarer phenotypes to have a fitness advantage, as they are less likely to be targeted by predators or diseases. Together, these mechanisms work to maintain genetic diversity and prevent any single allele from becoming fixed in the population.
• Evaluate the implications of balancing selection on evolutionary dynamics and its potential role in human health.
  • Balancing selection has significant implications for evolutionary dynamics as it promotes genetic diversity and adaptability within populations. In human health, this can be observed through traits such as the sickle cell gene providing malaria resistance, demonstrating how balancing selection can protect against specific diseases while maintaining other potential disadvantages. Understanding these dynamics is crucial for fields like medicine and conservation biology, as it informs strategies for managing genetic resources and addressing health disparities influenced by genetic variation.

Related terms

Heterozygote advantage: A form of balancing selection where individuals with two different alleles for a particular gene have a greater fitness than those with two identical alleles.

Negative frequency-dependent selection: A mechanism of balancing selection where the fitness of a phenotype decreases as it becomes more common, allowing rare phenotypes to thrive.

Genetic drift: The random fluctuation of allele frequencies in a population, which can affect genetic diversity, but is not a selective pressure like balancing selection.