In order to test many evolutionary hypotheses, it is necessary to have a good understanding of the phylogenetic history of the group being studied. Powell and colleagues have been exploring the use of modern molecular technology to determine genetic relatedness; in particular they have measured DNA differences among species. If one makes the assumption that species become more genetically dissimilar the longer they have been separated in evolutionary time, then these genetic distances reflect history and thus allow the construction of phylogenetic relationships. The group of organisms studied is the common "fruit fly" or, more properly, Drosophila. These flies have a long history in genetic and evolutionary studies and are beginning to play a large role in more modern studies in molecular evolution and development. The major project support by this renewal is an exploration of a new strategy to determine degree of genetic differences among species. Previous work has shown that Drosophila are extremely fast evolving with respect to changes in DNA. Even morphologically indistinguishable species may have very different DNA. Because of this rapid rate of evolution on the molecular (as opposed to morphological) level, it becomes difficult to compare distantly related species. This is because they may be so different one cannot distinguish homologous sequences; homologous sequences are those that are similar due to having a common origin. There is a part of the genome, however, which is relatively slowly evolving which may be more useful in comparing species. This is the portion of the genome which codes for proteins; it represents only a small part of the total genome, probably less than 10%. Powell and colleagues will isolate the protein coding region of the Drosophila genome and compare it among species. This will not only allow them to determine relationships among species, but also allow to compare how functionally different parts of a genome are evolving.
