| Summary: | This dissertation focuses on dioecious angiosperms with a genetic system of sex determination based on a pair of heteromorphic sex chromosomes. Silene latifolia and S. dioica (Caryophyllaceae), with their X/Y mechanism and heterogametic males, have become model organisms for the study of genetic sex determination in angiosperms. Random amplified polymorphic DNA (RAPD) markers provide a valuable tool for the study of the genetic nature of the male determining Y chromosome. We first embarked on a search for Y chromosome RAPD markers using the breeding technique of bulked segregant analysis, obtaining 101 Y chromosome markers which together, were shown to characterize the two species. Genetic mapping placed one of these Y chromosome molecular markers in the pseudoautosomal region of the sex chromosomes. This finding provides a tool for the study of recombination rates among sex chromosomes and relative rates of evolution of X and Y chromosomes. Finally, we investigated the molecular nature of a highly conserved Y chromosome marker and looked for homologous sequences in other related dioecious and hermaphroditic species. The marker of choice had been found to be conserved across males from four species of Silene, section Elisanthe. It was cloned, sequenced and analyzed by Southern hybridization. This Y chromosome marker is a high copy sequence that shares homology to female DNA. Forward and reverse primers were designed to amplify the male specific band only. The amplification pattern of the resulting sequence characterized amplified region (SCAR) in related taxa provide evidence for: (1) a common ancestry of the Y chromosomes of dioecious Silene, section Elisanthe, (2) a different branch of the evolution of dioecy in section Otites, (3) the distant relationship of the hermaphrodite S. noctiflora to the dioecious members of section Elisanthe and (4) homology between the Y chromosome of dioecious Silene dioica and autosomes of hermaphroditic S. flos-cuculi.
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