published_or_final_version / abstract / Botany / Doctoral / Doctor of Philosophy

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Of the 62 chromosome translocations in Gossypium hirsutum that have been isolated, made homozygous, identified as to the chromosomes involved, and maintained as homozygous tester lines, only T8-12 is phenotypically abnormal. Homozygotes are dwarf with a mutant "crumpled-mottled" phenotype that includes negligible fertility in field-grown plants; heterozygotes have a more normal morphology and variable fertility. The mutation has been reported to be tightly linked with the translocation and has never been separated from it. Comparative pollen viability, quantitative morphological measurements, and segregation data were used to dissociate the mutant phenotype from the T8-12 breakpoint--and from the mimic mutant, Crp. The T8-12 breakpoint was also demonstrated to be independent of the semilethal locus Lf on chromosome 12. Homozygous T8-12 and Crp individuals were shown to be morphological, but not functional, equivalents. Heterozygous and homozygous Crp plants produced essentially normal pollen; T8-12 heterozygotes had significantly reduced mean pollen viability scores. Mean bracteole measures were significantly different between T8-12 and Crp heterozygotes. The fluorescein diacetate-based fluorochrome reaction identified both chromosomal and genic effects on pollen viability in this study; the potential usefulness of the FCR method was thus extended to the level of single mutant gene effects.

Mitosis and meiosis of five Plantago species were analyzed. Plantago argyrea, P. patagonica and P. wrightiana contain 2n = 20 chromosomes and P. rhodosperma and P. virginica 2n = 24 chromosomes. Similar modes of evolution of the karyotypes of the 2n = 20 species are suggested. All species are presumed to be tetraploid, arising from 2n = 10 and 2n = 12 ancestors. Structural changes in the karyotype of 2n = 12 species could produce one or more large chromosomes resulting in a decrease in chromosomes from 6 to 5. Consequently, chromosome lengths in 2n = 10 and derived 2n = 20 species could be increased by addition of repetitive DNA along the length of each chromosome to maintain chromosome field. Chromosomes of 2n = 24 species are more symmetrical and presumably more primitive than the 2n = 20 species. Chiasma frequencies in meiotic cells of all five species are similar. This suggests that the majority of changes DNA content are in repetitive DNA.

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Thesis (Ph. D.)--University of Queensland, 2002. / Includes bibliographical references.

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