page_title: HKA test
section_title: Example
hierarchical_section_title: HKA test / Example
caption_attribution_description: English: See HKA Test Page
context_page_description: The HKA Test, named after Richard R. Hudson, Martin Kreitman, and Montserrat Aguadé, is a statistical test used in genetics to evaluate the predictions of the Neutral Theory of molecular evolution. By comparing the polymorphism within each species and the divergence observed between two species at two or more loci, the test can determine whether the observed difference is likely due to neutral evolution or rather due to adaptive evolution. Developed in 1987, the HKA test is a precursor to the McDonald-Kreitman test, which was derived in 1991. The HKA test is best used to look for balancing selection, recent selective sweeps or other variation-reducing forces.
context_section_description: For these examples, the distance between two species’ loci is determined by measuring the number of substitutions per site when comparing the two species. We can then calculate the rate of mutation (changes to the DNA sequence pre unit of time) if we know the time since the two species diverged from the common ancestor.
  A test that suggests neutral evolution:
  Suppose that you have data from two loci (1 and 2) in two species (A and B). Locus 1 shows high divergence and high polymorphism in both species. Locus 2 shows low divergence and low polymorphism. This can be explained by a neutral difference in the rate of mutations in each loci.
  A test that suggests selection:
  Again suppose you have data as in the last example, only this time locus 2 has equal divergence to locus 1 and yet lower polymorphism in species B. In this case the rate of mutation in each loci is equal, so this can only be explained by a reduction in the effective population size Ne of species B, which is inferred as an act of selection.
caption: Example of Directed Evolution - Selection
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