Studies in population genetics

This dissertation presents two independent studies in population genetics. The first is research on the population dynamics of multiple mating type laboratory cultures of the ciliate Tetrahymena hyperangularis. The second considers the form and relative importance of various types of knowledge involved in solving elementary population genetics problems.;Although it may be possible for students to develop simple skills such as reading technical terms, making mathematical computations, or remembering symbolic conventions, problem solving in population genetics is difficult for most to master. Based on a current knowledge model of mathematical problem solving, it was hypothesized that many difficulties could be attributed to inadequacies in schematic and strategic knowledge. Schematic knowledge, represented as a network of concepts, relations, and operators, was found to serve as a predictor of problem difficulty, an organizer of factual knowledge, a predictor of "expected" formulations, and a justifier of common "novel" formulations. Inadequacies in strategic knowledge, as indicated by analysis of 1690 solution paths, indicated that unsuccessful solutions are due to misuse of correct formulations or use of incorrect formulations in solving a problem.;Three mature stocks of Tetrahymena hyperangularis were mixed in unequal proportions establishing six two mating type and six three mating type mixtures. Most cultures mated soon after establishment as indicated by the presence of immature cells in the first sample. The proportion of immatures increased to 100% from which one infers that the progeny were more fit than their parents. When progeny lines became mature (62 + 19 days after mating), there was a lack of diversity of mating types. Regardless of the initial genotypic ratio, most cultures which had a mating type V allele yielded only mating type V cells in a sample of twelve cells taken four months after initiation. After four more months, some cultures which had previously appeared pure proved to have been heterogeneous, but others were apparently completely mating type V. The theoretical expectation of equal proportions of each mating type was not achieved. The dynamics of the mixed cultures was dominated by competition and selection for a particular genotype.