| An important task of evolutionary genetics is investigation of the possible relationships between functional properties of genes and their patterns of evolution. For example, given that evolutionary conflicts exist between pathogens and the immune systems of their hosts, host immune system genes might be expected to experience different evolutionary forces compared to many other types of genes. If true, we should expect to observe evidence of the pathogen-mediated selection pressures in the distribution of DNA sequence variation in host immunity genes within and between species. There is a good deal of population genetic evidence, especially in plants, that the evolution of host immunity proteins is driven by both directional and diversifying selection.;Much of the research on immunity gene evolution has focused on evidence for natural selection on proteins that interact directly with foreign cells or molecules, such as recognition and attack proteins. However, it is now widely accepted that pathogen genomes encode a wide array of immunomodulatory molecules that can interfere with host proteins involved in both extracellular and intracellular immunity signalling pathways. Thus, pathogen-mediated selection pressures may drive the evolution of several classes of host immunity proteins, including those linking recognition with attack.;Recent advances in the genetic and biochemical description of the Drosophila immune system have allowed for a molecular population genetic approach to infer the evolutionary histories of several components of the fruitfly immune system. Here polymorphism and divergence data from 34 Drosophila simulans genes thought to be involved in the immune response are presented. The goal is to determine the relative importance of directional selection, balancing selection, and genetic drift in determining the evolution of immune system proteins, and to investigate how these different forces are distributed across functionally distinct components of the immune system. |
