This project seeks to elucidate outstanding questions concerning rates of molecular evolution and the forces which determine these rates a model system for understanding molecular and the effects of DNA and protein changes. Understanding of these processes will contribute to the understanding of the human genome and the genetic variation within human populations. DNA sequences contain an enormous amount of information about the evolutionary relationships among organisms. One important heuristic tool for interpreting sequence information is the "molecular clock," but the properties of the clock are not well known. Critical information about the molecular clock will be obtained by sequencing approximately 2000 base pairs DNA from each of five loci from each of fifteen dipteran species. Some of the sequences will be analyzed in comparison to homologous sequences in humans and other mammals to investigate the rate of evolution over the whole sequence and with respect to particular regions and site (silent, replacement, intron and flanking sites) A variety of models of molecular evolution will be tested with the data.