Environmental effects on mutation have been documented for many years but have concentrated on agents that directly interact with DNA. Mutation research in its early history investigated a variety of more mundane environmental factors at levels that inhibited biological function and attempted to characterize their mutagenicity. This thesis revisits these old questions armed with more modern methods. It consists of one review chapter and three experimental chapters. The review chapter proposes that biological organization itself acts to direct mutation pressure, and that many mutations are context dependent within this organization. Experimentally, I performed an approximately 1,500-generation mutation accumulation (MA) experiment using the budding yeast Saccharomyces cerevisiae as an evolutionary genetic model. This thesis investigates the rates and distribution of effects of new mutations on fitness when they accumulate under a moderate salt stress. The first experimental section describes the production of the MA lines, measures the diploid fitness traits mitotic growth rate and sporulation, and uses changes in fitness among replicate lines to infer mutation parameters affecting these traits. Mutation rate estimates for these traits were roughly doubled in the salt stress treatment. The proportion of beneficial mutations was high for mutations affecting sporulation in both MA treatments but zero for growth rate. Measurements of haploid viability and haploid growth rate on strains derived from the diploid MA lines were used to infer mutation parameters. Mutation rates affecting haploid growth were ten-fold higher in our salt-line derivatives than those derived from the non-stress treatment. Variance component analysis identified a large fraction of genetic variation arising from differences among haploids within the same tetrad. This component was significantly larger in the salt MA treatment than the non-stress treatment. MA lines were subjected to a novel weak-acid stress. Mutation rate estimates were 38-fold higher in the salt MA treatment when lines were tested under acid stress. Cross-environmental genetic correlation for growth in acid stress versus standard media was significantly different between the two MA treatments suggesting that both MA environment and test environment are important factors when considering mutational effects on fitness.

No description available.

The posterior cytoplasm of the Drosophila melanogaster egg and early embryo is very important because it forms pole cells which are the precursors to the germ cells found in the adult gonads. The posterior portion has been irradiated by many investigators to destroy these pole cells and record the types of effects the deletion has on the developing embryo. A St. Margarita Island strain of D. melanogaster contains a naturally occurring mutation on the X chromosome which affects the development of germ cells in the offspring. This mutation is a semi-dominant, maternal effect, temperature sensitive mutant. In this study female offspring from this strain were examined after having their X chromosomes subjected to 15 generations of selection for expression of agametic gonads. The agametic ovaries of these individuals were examined at the dissecting microscope, light microscope, and electron microscope levels and compared with normal ovaries of Oregon-R wild type females. The mutant ovaries examined contained normal mesodermal components but appeared to lack any developing stem cells or egg chambers. It was concluded that the mutant gene(s) morphological effects occur between the time the pole cells are incorporated into the posterior midgut of the embryo during gastrulation and the time they reach the adult gonad.

The Rhizobium-legume symbiosis is an opportunistic association between two symbiotic partners that results in the formation of the root nodule. The process depends on the expression of a number of plant and bacterial genes that are considered critical for the establishment and maintainance of the symbiotic state. The merits of a mutational approach to the analysis of symbiosis have been recognized for several years and transposon Tn5 mutagenesis of Rhizobium has led to the identification of several symbiotic genes. This study describes the use of Tn5 mutagenesis for the isolation of symbiotically defective mutants of Bradyrhizobium japonicum. Two classes, auxotrophic and cell surface-altered mutants defective in nodule formation, have been characterized. In B. japonicum USDA 122, histidine auxotrophs that are defective in nodulation have been studied. The mutagenized DNA region has been cloned and the wild-type DNA region isolated by hybridization and complementation. In B. japonicum 61A76, Tn5-induced cell surface-altered mutants have been isolated by selecting for bacteriophage resistance. Several parameters have been used to demonstrate alterations in cell surface components. It has been shown that the Tn5 insertion is not the primary cause of the mutation in two of the characterized mutants. Complementation tests have led to the isolation of a wild-type DNA-containing cosmid, pPS23A, that overcomes the symbiotic defect in one of the mutants. Analysis of the cell surface showed a partial restoration of surface components in the complemented mutant.

Thesis (M. Phil.)--University of Hong Kong, 2007. / Also available online.

Diss. (sammanfattning) Uppsala : Sveriges lantbruksuniv., 2003. / Härtill 3 uppsatser.

Thesis (M. Sc.)--University of Canterbury, 2005. / Typescript (photocopy). Includes bibliographical references (leaves [96-108]). Also available via the World Wide Web.

Thesis (Ph.D.) - Carleton University, 2002. / Includes bibliographical references (p. 224-254). Also available in electronic format on the Internet.

Thesis (M. Phil.)--University of Hong Kong, 2007. / Title proper from title frame. Also available in printed format.

Thesis (Ph. D.)--University of Washington, 2004. / Vita. Includes bibliographical references (leaves 74-80).