Balancing Selection and Polymorphism Effects

Effects of Balancing Selection on Polymorphism Patterns

  • Introduction

    • Objective: Understand the effects of balancing selection on patterns of polymorphism.

    • Comparison: The study involves three effects analogous to those observed in selective sweeps.

First Effect of Balancing Selection

  • Overview

    • The initial effect pertains to the maintenance of genetic diversity within populations.

    • Implication of balancing selection: It preserves multiple alleles in a population, preventing one allele from becoming fixed.

Second Effect of Balancing Selection

  • Polymorphism Events

    • Focus on TMS (total molecular diversity) represented as positive in specific regions.

  • Population Structure Example

    • Example of two separate populations:

    • Population One and Population Two:

      • Defined by physical barriers (e.g., mountains, rivers), preventing gene flow.

    • Mutation Differentiation:

    • Population One accumulates different mutations compared to Population Two, which experiences different genetic drift events.

    • Upon removing the physical barrier, the interaction of these previously isolated populations leads to a higher degree of intermediate frequency polymorphisms.

Third Effect of Balancing Selection

  • Balanced Polymorphism Example in Drosophila

    • Examines two alleles in fruit flies:

    • Fast Allele (ABHF)

    • Slow Allele

    • Experiments can be conducted in the laboratory to compare the functional differences between these alleles.

    • A key distinction between them relates to their performance under different environmental conditions.

  • Geographical Variances

    • In warmer climates, typically a higher frequency of slow alleles is observed.

    • Contrasting conditions may show different allele frequencies, suggesting varying environmental pressures.

Mechanisms of Allele Maintenance

  • Evolutionary Forces

    • Suggests the presence of an evolutionary mechanism that maintains both alleles in gene flow, indicative of balancing selection.

    • Illustrates how balancing selection can lead to adaptive advantages depending on environmental conditions.

Conclusion

  • Mutation Impact

    • Discusses the effect of a specific mutation (from C to T) on allele frequency and adaptability.

    • Potential influences include:

    • Positive selection.

    • Random genetic drift.

    • Outcome: This new mutation may increase diversity and contribute to the overall polymorphism observed in the population.