Balancing selection

Definition

Balancing selection is a type of natural selection that maintains genetic diversity within a population by favoring the survival of multiple alleles at a particular locus. This process helps preserve variations in traits that can be beneficial under different environmental conditions, leading to a dynamic equilibrium of allele frequencies. In this way, balancing selection plays an essential role in shaping evolutionary paths and promoting adaptability in changing environments.

5 Must Know Facts For Your Next Test

1. Balancing selection can occur through mechanisms like heterozygote advantage, where the presence of both alleles improves survival and reproduction.
2. This type of selection is important in maintaining polymorphisms, which are the occurrence of two or more clearly different phenotypes within the same population.
3. One classic example of balancing selection is seen in the sickle cell trait, where individuals with one sickle cell allele have increased resistance to malaria.
4. Balancing selection often results in stable allele frequencies over time, rather than driving one allele to fixation.
5. Environmental changes can shift the selective pressures on certain alleles, potentially altering the balance of selection and affecting genetic diversity.

Review Questions

• How does balancing selection contribute to genetic diversity within a population?
  • Balancing selection promotes genetic diversity by favoring multiple alleles at a locus, allowing for various phenotypes to coexist. This can lead to greater adaptability as different alleles may provide advantages under changing environmental conditions. By maintaining these variations, populations are better equipped to survive challenges such as diseases or climate shifts.
• What is the relationship between heterozygote advantage and balancing selection, and how does this affect allele frequencies?
  • Heterozygote advantage is a key mechanism of balancing selection, where individuals carrying two different alleles at a locus have higher fitness compared to those with two identical alleles. This results in the maintenance of both alleles within the population rather than allowing one to dominate or become fixed. Over time, this creates stable allele frequencies and ensures that genetic variation is preserved.
• Evaluate how environmental changes can impact balancing selection and potentially alter the genetic landscape of populations.
  • Environmental changes can shift selective pressures acting on specific alleles, which may disrupt the equilibrium established by balancing selection. For instance, if a new disease emerges that targets individuals with a previously advantageous allele, the fitness landscape may change, leading to an increased frequency of another allele that provides better resistance. This dynamic nature highlights how balancing selection is not static; it adapts to external influences and plays a crucial role in shaping the evolutionary trajectories of populations.

Related terms

heterozygote advantage: A phenomenon where heterozygous individuals at a specific gene locus have a higher fitness than either homozygous genotype, often seen in balancing selection.

frequency-dependent selection: A form of selection where the fitness of a phenotype depends on its frequency relative to other phenotypes in a given population, which can contribute to maintaining genetic variation.

genetic drift:

A mechanism of evolution that involves random changes in allele frequencies within a population, which can affect the outcome of balancing selection.