McDonald-Kreitman Test

Definition

The McDonald-Kreitman test is a method used in evolutionary biology to compare the rates of polymorphism (variation within a population) and divergence (variation between species) at protein-coding genes. This test helps to assess the role of natural selection in shaping genetic variation by examining differences in allele frequencies between species and within populations. It is particularly useful for determining whether certain alleles are being favored or selected against in a given environment.

5 Must Know Facts For Your Next Test

1. The McDonald-Kreitman test compares synonymous (neutral) and non-synonymous (adaptive) substitutions to identify the action of natural selection on protein-coding genes.
2. If there is an excess of non-synonymous substitutions compared to synonymous ones, it may indicate positive selection acting on those alleles.
3. Conversely, if there are more synonymous than non-synonymous substitutions, it suggests that purifying selection is likely at play, removing deleterious mutations.
4. The test can be applied across various taxa to investigate evolutionary pressures in different environments and contexts.
5. Statistical analyses and models are often employed alongside the McDonald-Kreitman test to better understand the underlying forces driving observed genetic patterns.

Review Questions

• How does the McDonald-Kreitman test provide insights into the effects of natural selection on genetic variation?
  • The McDonald-Kreitman test allows researchers to analyze the balance between synonymous and non-synonymous substitutions in protein-coding genes. By comparing polymorphism within populations to divergence between species, this test reveals whether certain alleles are being positively selected or purged from the gene pool. If non-synonymous substitutions are found to be significantly higher than expected under neutral evolution, it indicates that those alleles may confer some adaptive advantage.
• Discuss how the results of the McDonald-Kreitman test can influence our understanding of evolutionary processes across different species.
  • Results from the McDonald-Kreitman test can illuminate how evolutionary pressures vary across species and environments. For example, if one species exhibits a high rate of non-synonymous substitutions relative to another, it suggests that different selective pressures are acting on those populations. This comparative approach helps researchers understand how adaptation occurs in response to ecological changes and can highlight the molecular basis of evolution in diverse contexts.
• Evaluate the implications of using the McDonald-Kreitman test in conservation genetics and its potential applications.
  • Using the McDonald-Kreitman test in conservation genetics can have significant implications for understanding how populations adapt to changing environments or anthropogenic pressures. By identifying alleles under positive selection, conservationists can prioritize genetic diversity in their management strategies. Additionally, understanding which genes are subject to natural selection can inform breeding programs aimed at enhancing resilience against diseases or climate change effects, ensuring the long-term survival of endangered species.

Related terms

Polymorphism: The occurrence of two or more different alleles at one locus in a population, contributing to genetic diversity.

Divergence: The accumulation of differences between groups, often leading to speciation as populations evolve separately over time.

Natural Selection:

The process through which traits that enhance survival and reproduction become more common in a population over generations.