A Tutorial of the Poisson Random Field Model in Population Genetics

Selectionists and neutralists have fiercely debated, for the past five decades, the extent to which Darwinian selection has shaped molecular evolution. However, both camps do agree that Darwinian selection is a bona fide natural phenomenon. Therefore, various so-called "tests of neutrality" have been developed to detect natural selection on a particular gene or genomic location (for a review on this topic, see Biswas and Akey, 2006). However, these tests are often qualitative and only provide the directionality of selection. A decade and a half ago, S. Sawyer and D. Hartl provided a mathematical framework with which to determine quantitatively the intensity of selection on a particular gene, which they applied to the Adh locus in the Drosophila genome (Sawyer and Hartl, 1992).