The three experiments to be conducted address basic questions about the forces that shape genetic variation in populations. Drosophila is the model organism because it is will studied and highly suitable for molecular approaches. Recent work has revealed that there is remarkably little molecular polymorphism in regions of the genome that have relatively little genetics recombination. The most promising theory to account for this is that favorable mutants occasionally move through the population, removing polymorphisms in a large region that lacks recombination. The proposed experiments attempt to test some of the quantitative predictions of this theory. Another experiment investigates whether polymorphism is a "process pseudogene." Since this type of gene is thought to have no function, the study of such a gene will give important baseline data on a part of the genome that is "free" from the force of natural selection. The third experiment is designed to test a prediction of a theory that accounts for the containment of copy numbers of transposable elements (DNA parasites) in natural populations. This theory and the observed distributions of transposable elements predicts that there will be high levels of unequal crossing over near the tips of the X chromosome in Drosophila. The proposed experiments will directly measure the frequency of unequal (ectopic) exchange in this region of the genome. The results from these experiments should advance our theoretical understanding of the impact of various recombinational and mutational processes on standing variation. This theoretical area of knowledge is often the foundation for the interpretation of practically important and/or theoretically interesting genetic variation in humans and other organisms of economic or basic interest.
