McDonald-Kreitman Test

Definition

The McDonald-Kreitman test is a statistical method used to assess the effects of natural selection on protein-coding genes by comparing the rates of synonymous and nonsynonymous mutations. This test provides insights into whether a gene has undergone adaptive evolution, as it evaluates the differences in mutation rates in both conserved and variable regions of a gene, which can indicate the strength of selection acting on it.

5 Must Know Facts For Your Next Test

1. The McDonald-Kreitman test relies on the comparison of observed mutation rates to expected rates under neutral evolution, helping to identify deviations that suggest selective pressure.
2. A key aspect of the test is analyzing polymorphism data (within a population) alongside divergence data (between species), which helps distinguish between neutral and selected changes.
3. When there are significantly more nonsynonymous substitutions than expected, it suggests positive selection has acted on the gene in question.
4. Conversely, if synonymous mutations dominate, it might indicate stabilizing selection or purifying selection maintaining the function of the gene.
5. The McDonald-Kreitman test can be applied to various taxa, providing valuable insights into evolutionary dynamics across different species and environments.

Review Questions

• How does the McDonald-Kreitman test differentiate between neutral evolution and adaptive evolution?
  • The McDonald-Kreitman test distinguishes between neutral evolution and adaptive evolution by comparing synonymous and nonsynonymous mutation rates. If nonsynonymous mutations are significantly higher than expected under neutral conditions, it suggests that these mutations are favored by natural selection, indicating adaptive evolution. In contrast, if synonymous mutations are more prevalent, it indicates a lack of strong selective pressure, supporting a neutral evolutionary scenario.
• Discuss how the data from polymorphism and divergence can be utilized in the McDonald-Kreitman test to infer selection patterns.
  • In the McDonald-Kreitman test, data from both polymorphism within a population and divergence between species are analyzed together. Polymorphism data reveals genetic variation among individuals within a species, while divergence data highlights differences between closely related species. By comparing these two datasets, researchers can assess whether observed differences in mutation rates align with expectations under neutrality or suggest selective pressures acting on specific mutations. This comparative approach allows for a more nuanced understanding of evolutionary dynamics.
• Evaluate the implications of applying the McDonald-Kreitman test across different species. What challenges and insights might arise?
  • Applying the McDonald-Kreitman test across different species can reveal insights into how evolutionary pressures vary among taxa and environments. However, challenges may include accounting for differences in mutation rates and environmental factors that influence selection. Additionally, interpreting results requires careful consideration of the evolutionary history and demographic factors specific to each species. Despite these challenges, the test offers valuable comparative data that enhances our understanding of adaptive evolution and informs conservation strategies by highlighting genes under selection.

Related terms

Synonymous Mutation: A mutation that does not change the amino acid sequence of a protein, often considered neutral in terms of evolutionary impact.

Nonsynonymous Mutation: A mutation that results in a change in the amino acid sequence of a protein, potentially affecting the protein's function and subject to natural selection.

Adaptive Evolution: Evolution that results in a better fit between organisms and their environment, often driven by natural selection acting on advantageous traits.