Cell cultures were examined for percentage of fragile sites seen in straight-stained, Q-stained and reverse fluorescent-stained preparations. In all cases, percentage of fragile site expression was decreased when compared to straight-stained preparations. However, fragile sites seen in Q- and RF-stain could be identified as on X chromosomes.

Canary grasses (Phalaris, Poaceae) include 21 species widely distributed throughout temperate and subtropical regions of the world with centers of diversity in the Mediterranean Basin and western North America. The genus contains annual/perennial, endemic/cosmopolitan, wild, and invasive species with basic numbers of x=6 (diploid) and x=7 (diploid/tetraploid/hexaploid). The latter display vastly greater speciation and geographic distribution. These attributes make Phalaris an ideal platform to study species diversification, dispersal, historic hybridization, polyploidy events, and chromosome evolution in the grasses. This body of research presents the first molecular phylogenetic and phylogeographic reconstruction of the genus based on the nuclear ITS and plastid trnT-F DNA regions allowing species relationships and the importance of polyploidy in speciation to be assessed. Divergence dates for the genus were determined using Bayesian methods (BEAST, version 1.6.2) and historic patterns of dispersal were analyzed with RASP (version 2.1b). Self-incompatibility and the feasibility of hybridization between major groups within the genus were studied with a series of greenhouse experiments. Acetocarmine and fluorescent staining techniques were used to study the morphology of the chromosomes in a phylogenetic context and the nuclear DNA content (C values) was quantified using flow cytometry. Four major clades were revealed in the genus with cytological and geographic affinities leading to the establishment of two subgenera and four sections in the first comprehensive infrageneric treatment of Phalaris. Divergence dating revealed a Miocene emergence (20.6-8.4 MYA) for the genus which is concurrent with studies of other genera in the Aveneae tribe. The hypothesis stating that Phalaris originated in the Mediterranean Basin and dispersed to the New World via a western route leading to a secondary center of diversification in western North America was supported by phylogeographic and cytological analyses. An empirical study comparing the weight, length, and width of the florets by morphological type and cytotype revealed significant differences that support a dispersal advantage among the New World and Arundinacea species. The x=6 species displayed greater intraspecific C value variation, higher DNA content per haploid chromosome set, and a distinct karyotype compared with the x=7 species indicating a complex history of chromosome evolution. / Ph. D.

<p> The ɣ-radiosensitivity of haploid and diploid Oedogonium cardiacum cells was measured and compared to other cell lines. With the doubling of the chromosome complement, the Do value doubled, but the extrapolation number decreased four-fold. A general conclusion was drawn from the results that at all doses of ɣ-radiation, the diploids were more resistant than the haploids. A new radiation technique was used and compared to that used routinely in the laboratory. The further use of the technique was not recommended since the data obtained with the diploid line only was not as reliable as one would like.</p> <p> The degree of synchrony of Oe. cardiacum zoospore cultures was measured using cell division as the biological end-point and a mathematical expression, the percent phasing, as the index of synchrony. It was intended that this research problem be secondary to the radiation studies. The percent phasing values were determined for cells growing in two inorganic media and in the presence of an inhibitor, hydroxyurea. However the degree of synchrony was not improved beyond that of the routine laboratory procedure. Attempts to improve the size of the synchronous populations collected also proved unsuccessful.</p> / Thesis / Master of Science (MSc)

<p> The mode of chromosome duplication during meiosis and mitosis in Haplopappus gracilis was investigated. Tritiated thymidine was incorporated into the pollen mother cells during premeiotic interphase, and the cells were allowed to reach the tetrad stage. The autoradiographs prepared from the tetrads showed an unequal distribution of grains over their nuclei, suggesting a conservative mode of chromosome duplication during meiosis. Seedlings were fed with tritiated thymidine for the duration of one cell cycle and also for the duration of several cell cycles. The autoradiographs prepared from the root tip cells, thus treated, showed both labelled and unlabeled chromatids in the anaphases of all the experiments, thus again suggesting a conservative mode of chromosome duplication. A chromosome model to explain the results is discussed. </p> / Thesis / Doctor of Philosophy (PhD)

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Unlike most RNA and DNA containing viruses, which induce cytogenetic damage at random sites throughout the human genome, the highly oncogenic adenovirus type 12 is also capable of inducing damage at specific chromosomal sites. Infection of human embryonic retinal or kidney cells with Ad12 results in the induction of heterochromatic gaps at specific (17q21-22, 1p36, 1q21, and 1q42-43) and random sites in the cellular chromosome. Previous work by Durnam et al. (1986) demonstrated that the viral early region 1 (E1) is sufficient for the induction of damage at band 17q21-22. The objective of the present study was to 1) identify the Ad12 E1 gene product(s) required for the induction of aberrations in human diploid cells, and 2) to determine whether the same or different functions are involved in the induction of damage at specific and random sites. To this end, adenovirus type 12/adenovirus type 5 recombinants with hybrid E1 sequences as well as viruses with mutations in the Ad12 E1B genes were used to map the Ad12 E1 function(s) required for the induction of chromosomal aberrations. The results of this study indicate that the expression of E1A proteins is not sufficient for this effect. On the other hand, mutations within the E1B 55Kd protein but not the E1B 19Kd protein were found to affect the ability of the virus to induce both specific and random damage (Schramayr et al., 1990). / Thesis / Master of Science (MS)

Expression of the Simian Virus 40 (SV40) early region in human cells results in the induction of chromosomal aberrations and polyploidy, and in transformation. To understand how genetic damage occurs and what role it plays in transformation, human diploid fibroblasts and embryonic kidney cells were transfected with plasmids encoding wild type or mutant forms of the viral early region, and the neo gene. Clones selected for G418 resistance and expressing viral genes were initially analyzed within 20 cell divisions. The results of this study demonstrate that expression of the SV40 large T antigen is sufficient for the induction of chromosomal damage and ploidy changes, and that small t does not contribute to these processes. Mutant plasmids either lacking the SV40 origin of DNA replication, or encoding a large T mutant defective in its ability to bind the retinoblastoma gene product (Rb) were as proficient as wild type plasmids, indicating that both viral DNA replication and binding of T antigen to Rb are not required for cytogenic damage. On the other hand, preliminary results with a plasmid encoding a T antigen mutant unable to bind the cellular p53 protein suggest that formation fo this complex may be important for cytogenetic damage. This study has also shown that chromosomal aberrations, but not necessarily polyploidy, increase in frequency and complexity upon subculturing of the clones regardless of whether such populations arrest at crisis or yield immortal lines. These results are compatible with the hypothesis that large T antigen destabilizes the cellular genome, and that specific mutations arising from this process may contribute to cell immortalization. / Thesis / Master of Science (MS)