The goal of this work is to contribute to the understanding of the genetics and evolution of natural populations. The mathematical knowledge of the amount and pattern of genetic diversity under various conditions is essential for the choice and design of experiments and for the investigation by computer of very complex systems. Comparison of relatively simple models with observations yields information about particular populations, and many such comparisons indicate the relative importance and conditions of action of the basic evolutionary forces. The latter include natural selection, mutation, migration, and random fluctuations in the proportions of various genes. All of these will be studied in this project. The evolution of repeated DNA sequences under gene conversion (the nonreciprocal transfer of information between genes) will also be investigated. In the long run, studies of genetic variability of the type proposed here provide information that helps to preserve and manage wild animals and plants. They also advance areas of the genetics of human populations that concern the frequency of genetic diseases, which are of immense medical importance.