McDonald-Kreitman Test

Definition

The McDonald-Kreitman test is a method used to analyze the patterns of genetic variation within and between species to infer the presence of natural selection. By comparing the ratio of polymorphisms (within species) to fixed differences (between species) at a specific locus, this test helps differentiate between positive selection and neutral evolution, shedding light on evolutionary processes.

5 Must Know Facts For Your Next Test

1. The McDonald-Kreitman test compares the number of synonymous and non-synonymous mutations to assess whether natural selection is acting on a specific gene.
2. A significant difference in the ratios of polymorphism to fixed differences suggests positive selection has acted on that gene.
3. If the ratios are similar, it indicates that evolution at that locus may be primarily neutral, not influenced by selection.
4. The test can provide insights into adaptive evolution by identifying genes that have undergone recent positive selection.
5. This method has been widely used in evolutionary biology to study various organisms, helping to uncover the dynamics of natural selection.

Review Questions

• How does the McDonald-Kreitman test differentiate between positive selection and neutral evolution?
  • The McDonald-Kreitman test differentiates between positive selection and neutral evolution by analyzing the ratio of polymorphisms within a species to fixed differences between species at a specific locus. A high ratio of non-synonymous polymorphisms relative to fixed differences suggests that positive selection is at work, as these variants confer an advantage. In contrast, a similar ratio indicates that mutations may be evolving neutrally without selective pressure, thus highlighting the evolutionary dynamics at play.
• Discuss the implications of findings from the McDonald-Kreitman test in understanding adaptive evolution in populations.
  • Findings from the McDonald-Kreitman test have significant implications for understanding adaptive evolution. When the test reveals evidence of positive selection, it suggests that certain genes are undergoing changes that enhance fitness in specific environments. This information can help researchers identify key adaptations within populations and understand how these changes contribute to survival and reproduction in changing environments. Furthermore, it can guide conservation strategies for endangered species by identifying critical adaptive traits.
• Evaluate how the application of the McDonald-Kreitman test has advanced our knowledge of evolutionary processes across different taxa.
  • The application of the McDonald-Kreitman test has greatly advanced our knowledge of evolutionary processes by providing robust evidence for natural selection across different taxa. This method has been instrumental in revealing how genetic variations influence adaptation to environmental pressures, aiding researchers in understanding patterns of evolution in diverse organisms from plants to animals. By highlighting specific genes under positive selection, it helps unravel complex interactions between genetics and ecology, contributing to a deeper comprehension of biodiversity and evolutionary mechanisms throughout history.

Related terms

Polymorphism: The occurrence of two or more different alleles at a locus within a population, indicating genetic variation.

Neutral Theory of Molecular Evolution: The hypothesis that most evolutionary changes at the molecular level are caused by random drift of mutant alleles that are selectively neutral.

Positive Selection:

A process in which advantageous genetic variants increase in frequency within a population due to their beneficial effects on fitness.