Chromosome evaluations were made on leukocyte blood samples from 169 phenotypically normal nulliparous Holstein heifers. These were from three different reproduction groups collected in sets of threes from 10 different herds in the western United States. Group 1, the control group, consisted of heifers diagnosed pregnant after one or two breedings; Group 2 consisted of heifers diagnosed pregnant after three or four breedings; and Group 3 consisted of heifers diagnosed open after four or more breedings. Metaphase chromosome spreads used in these analyses were obtained through 72-hour leukocyte cultures from heparinized whole blood. Processed cells were dropped onto a slide, air-dried, and stained with Giemsa. Chromosomes were then counted and X chromosomes were identified. A total of 1, 597 cells was evaluated, with 1,439 cells having counts of 60 chromosomes each. Thirty cells had less than 58 chromosomes, 31 cells had 58 chromosomes, 75 cells had 59 chromosomes, 14 cells had 61 chromosomes, and 8 cells had more than 61 chromosomes (9 .98% were different than 60). All counts of other than 60 chromosomes were isolated cases and were not identified as abnormalities. Only two cells from two separate heifers contained what may have been sex chromosome abnormalities. No persistent chromosomal defects were observed among the 169 heifers.

The main goal of this research is to understand molecular mechanisms of GAA/TTC-associated genetic instability in a model eukaryotic organism, S. cerevisiae. We demonstrate that expanded GAA/TTC repeats represent a threat to eukaryotic genome integrity by triggering double-strand breaks and gross chromosomal rearrangements. The fragility potential strongly depends on the length of the tracts and orientation of the repeats relative to the replication origin and to block replication fork progression. MutSbeta complex and endonuclease activity of MutLalpha play an important role in facilitation of fragility. In addition to GAA/TTC triplex forming repeats, non-GAA polypurine polypyrimidine mirror repeats that are prone to the formation of similar structures were found to be hotspots for rearrangements in humans and other model organisms. These include H-DNA forming sequences located in the major breakpoint cluster region at BCL2, intron 21 of PKD1, and promoter region of C-MYC. Lastly, we have investigated the effect of the triplex-binding small molecules, azacyanines, on GAA-mediated fragility using the chromosomal arm loss assay. We have found that in vivo, azacyanines stimulate (GAA/TTC)-mediated arm loss in a dose dependent manner in actively dividing cells. Azacyanines treatment enhances the GAA-induced replication arrest. We discovered that also, azacyanines at concentrations that induce fragility also inhibit cell growth. Over 60% of yeast cells are arrested at G2/M stage of the cell cycle. This implies an activation of DNA-damage checkpoint response.

published_or_final_version / Pathology / Doctoral / Doctor of Philosophy

No description available.

Chromosomal rearrangements play a major role in the evolution of eukaryotic genomes. Genomic aberrations are also a hallmark of many tumors and are associated with a number of hereditary diseases in humans. The presence of repetitive sequences that can adopt non-canonical DNA structures is one of the factors which can predispose chromosomal regions where they reside to instability. Palindromic sequences (inverted repeats with or without a unique sequence between them) that can adopt hairpin or cruciform structures are frequently found in regions that are prone for gross chromosomal rearrangements (GCRs) in somatic and germ cells in different organisms. Direct physical evidence was obtained that double-strand breaks (DSBs) occur at the location of long inverted repeats, a triggering event for the genomic instability. However, the mechanisms by which palindromic sequences lead to chromosomal fragility are largely unknown. The overall goal of this research is to elucidate the mechanisms of DSB and GCR generation by palindromic sequences in yeast, Saccharomyces cerevisiae.

Copies of author's previously published works inserted. / Bibliography: leaves 321-370. / xv, 370, [21] leaves : ill. (chiefly col.) ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / The aim of the project presented in this thesis is to isolate microsatellite markers and to construct a high resolution genetic map of the human X chromosome using these and pre-existing microsatellite markers. AC dinucleotide repeat markers are isolated from a bacteriophage library for application to the genetic localisations of X-linked disease genes, particularly those responsible for non-specific mental retardation (MRX). The genetic map is used to refine the location of the disease gene segregating in five families affected with X-linked mental retardation. / Thesis (Ph.D.)--University of Adelaide, Dept. of Genetics, 1997

Typescript (Photocopy) / Includes published papers co-authored by the author at the end of volume 2 / Bibliography: leaves 195-237 of vol. 1 / 2 v. : ill ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Thesis (Ph.D.)--Dept. of Paediatrics, Faculty of Medicine, University of Adelaide, 1991

Thesis (Ph. D.)--University of Hong Kong, 2007. / Also available online.

Thesis (Ph. D.)--University of Adelaide, Dept. of Paediatrics, 1994. / Errata slip inserted at back. Includes bibliographical references (leaves 159-192).

Thesis (Ph. D.)--University of Alabama at Birmingham, 2006. / Additional advisors: Vithal K. Ghanta, Denise R. Shaw, Stephen A. Watts, Bradley K. Yoder. Description based on contents viewed Feb. 20, 2009; title from PDF t.p. Includes bibliographical references.