Fay and Wu's H Test

Definition

Fay and Wu's H Test is a statistical method used to detect the presence of positive or negative selection in genetic data by analyzing the distribution of polymorphism and divergence at a given locus. This test focuses on the ratio of polymorphism within a population to divergence between populations, helping to identify deviations from neutral expectations that might suggest adaptive evolution or purifying selection. The test is particularly valuable in understanding how evolutionary forces shape genetic variation.

5 Must Know Facts For Your Next Test

1. Fay and Wu's H Test is based on the expectation that under neutral evolution, the amount of polymorphism should correlate positively with divergence between populations.
2. A significantly negative value of H indicates an excess of low-frequency polymorphisms, suggesting the possibility of positive selection acting on a locus.
3. Conversely, a significantly positive value of H indicates an excess of high-frequency polymorphisms, which may point to negative selection or demographic expansion.
4. The test assumes that populations are in equilibrium with respect to mutation and genetic drift, which means deviations from this can affect results.
5. This method can be applied to various species and genomic regions, making it versatile for studying evolutionary dynamics across different contexts.

Review Questions

• How does Fay and Wu's H Test differentiate between positive and negative selection based on polymorphism data?
  • Fay and Wu's H Test differentiates between positive and negative selection by comparing the amount of genetic polymorphism within a population to the genetic divergence observed between populations. A significantly negative H value suggests an excess of low-frequency variants, which is often indicative of positive selection acting on advantageous mutations. In contrast, a positive H value suggests an excess of high-frequency variants, typically pointing towards negative selection or demographic events like population bottlenecks.
• What assumptions must be met for Fay and Wu's H Test to yield reliable results regarding evolutionary processes?
  • For Fay and Wu's H Test to provide reliable insights into evolutionary processes, several assumptions must be met. Firstly, it is assumed that the populations being compared are in equilibrium with respect to mutation rates and genetic drift. Additionally, it is important that the loci analyzed are not subject to strong selective pressures other than those being investigated. Violations of these assumptions can lead to misinterpretation of the test results, impacting conclusions about positive or negative selection.
• Evaluate the implications of using Fay and Wu's H Test in population genomics studies for understanding evolutionary dynamics across species.
  • Using Fay and Wu's H Test in population genomics studies has significant implications for understanding evolutionary dynamics across different species. The ability to detect positive or negative selection provides insights into how species adapt to changing environments and respond to selective pressures. This information can inform conservation strategies by identifying genetic loci that are critical for survival. Furthermore, analyzing multiple loci across species allows researchers to compare adaptive responses and evolutionary histories, enhancing our understanding of biodiversity and evolutionary mechanisms at a broader scale.

Related terms

Polymorphism: The occurrence of two or more genetically distinct forms within a population, often measured by the frequency of alleles at a given locus.

Divergence: The genetic differences that accumulate between populations over time due to evolutionary processes, such as mutation, selection, and genetic drift.

Selection Pressure: The environmental factors that influence which individuals in a population are more likely to survive and reproduce, thereby affecting the frequency of traits in the next generation.