| Summary: | 碩士 === 國立清華大學 === 分子與細胞生物研究所 === 93 === Genetic evidence shows that the genes contributing to hybrid male sterility evolve rapidly. Molecular data also suggest that these genes were under positive selection during species differentiation. Since hybrid sterility has no obvious adaptive significance, it must be the byproduct of nature selection for differential adaptation. Odysseus (OdsH) is a hybrid male sterility gene between Drosophila simulans and D. mauritiana. Previous studies showed that the D. melanogaster males of OdsH0 produce fewer progenies than wild-type males do. In order to understand the evolution of hybrid sterility genes, the fitness of different alleles of OdsH by transgenic approach was analyzed. The results showed that the fertility defect of OdsH[0] can be rescued by OdsH[mel] transgene and that normal males carrying an extra copy of OdsH[mel] produce more offspring than wild-type ones do. Males with hetero-specific (OdsH[sim] and OdsH[mau]), but not paralogous (unc-4), transgenes show increased fertility like the ones with OdsHmel. I also proved evidences to support the idea that the function of OdsH was to accelerate sperm regeneration. The importance of OdsH is emphasized under multi-mating, which is a more likely scenario occurred in the nature. Therefore, the hybrid male sterility genes, such as OdsH, can have significant impact in fitness and are subjects to natural selection. Moreover, I also demonstrate that the issue of functional redundancy of OdsH and unc-4 can be further addressed by generating mutants via gene targeting.
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