Thesis--Johns Hopkins University.

Thesis (Ph. D.)--University of Chicago. / Reprinted from the first series, v. 10 (p. 73-[77]) of the Decennial publications of the University of Chicago. Includes bibliographical references. Also available on the Internet.

Thesis (Ph. D.)--University of Chicago. / Reprinted from the first series, v. 10 (p. 73-[77]) of the Decennial publications of the University of Chicago. Includes bibliographical references.

Thesis (Ph. D.)--Johns Hopkins University, 1914. / Vita. "Reprinted from the Journal of Experimental Zoology, vol. 19, no. 2. August, 1915." "Literature cited": p. 205-207.

Thesis--Johns Hopkins University.

Thesis (Ph. D.)--University of Michigan, 1933. / Cover title. Thesis note on label mounted on p. 271. "Reprinted from Transactions of the American microscopical society, vol. LII, no. 4, October,1933." "Literature cited": p. 312-313.

Populations of Chlamydomonas were maintained in a benign laboratory environment as obligatory sexual or asexual populations for five years. Sexual reproduction is expected to facilitate the elimination of mildly deleterious mutations and thereby increase the mean fitness of a sexual population relative to an asexual population (Kondrashov 1988). Fitness in competition and in pure culture was measured. In neither of the fitness assays, both in solid and liquid cultures of Chlamydomonas, was a fitness advantage of sexual reproduction seen, even though the results varied depending on the definition of fitness. I hypothesized that the effect of mutation clearance could be masked by different forces acting on the selection strain (such as an antagonistic relationship between sexual and vegetative fitness).

No description available.

Since their discovery, transposable elements (TEs) have been regarded either as useful building blocks of genomes, or as "selfish DNA": genetic parasites that exploit the sexual cycle to spread in copy number within populations to the detriment of their hosts. If the "selfish DNA" hypothesis is correct, TEs are expected to deteriorate and be lost from asexual populations. This thesis tests the predictions of the "selfish DNA" hypothesis in four asexual plant species, focusing on patterns of nucleotide diversity and nucleotide substitution. Sequences bearing strong resemblance to known TE families including Ty1/copia, Ty3/gypsy, and LINE-like elements were successfully isolated from all four plant species, and showed patterns of nucleotide substitution consistent with a long history of purifying selection. Stochastic simulations were also conducted, and suggested that this result is expected if the host species has been asexual for less than tens of thousands of generations.

No description available.