9527808 GILLESPIE The goal of many studies of molecular evolution is to understand why there is so much variation in the genetic material, DNA, between species and between individuals within a species. In one theory most of this variation has no functional consequences. In the theory being studied in this project, most of this variation does have biological consequences. To understand which theory and assumptions best describe molecular evolution, the predictions of each theory will be compared with the patterns observed in actual DNA sequences. This work is of potential value for understanding genetic variation in such traits as disease susceptibility in human populations. Is genetic variation in susceptibility due to many small mutations or to a few large ones? The goal of the second part of this project, on quantitative genetics, is to understand the genetic basis of variation in measurable traits, such as size or weight, both within and between species. The great conceptual problem in this work is to deal with the combined effects of many genes, each of small effect, on a quantitative trait. In the theory to be investigated these small genes interact with one another in a way that adds biological relevance that was missing from previous models. Once the theory is in place, it will be used to investigate several problems of biological interest. This work will be important for agriculture, where practitioners require better theories of the genetic basis of traits, such as milk yield in cattle, that are of economic importance.
