根據遺傳學上的證據顯示，雜交雄性不孕相關之基因具有快速演化的現象。分子證據認為這些快速演化的基因可能是因為在物種分化的過程中受到天擇作用。但由於雜交不孕的基因對於個體的生存並沒有明顯優勢，因此雜交不孕的現象一定是某個被天擇作用的基因所衍生來的副產物。對於Drosophila simulans和D. mauritiana而言，Odysseus (OdsH)是一個雜交雄性不孕基因。在D. melanogaster中的研究顯示，若雄果蠅缺少OdsH這個基因，其所產生的後代數目會比正常的雄果蠅少。為了了解雄性不孕基因的演化，藉由轉殖基因的方式分析不同OdsH對偶基因的適合度(fitness)，而結果顯示原本因突變而造成在繁殖力上的傷害可被同種的OdsH對偶基因(OdsH[mel])恢復，而且當正常的雄果蠅又多擁有一套OdsH[mel]時將可以產生更多的後代。而雄果蠅若是擁有異種對偶基因(OdsH[mel]及OdsH[mau])也會具有較好的繁殖能力，但如果帶有相似型的轉殖基因(paralogous allele, unc-4)則看不到此現象。另外我們也提供證據認為OdsH是藉由加速精子的形成來提高它的適合度。在自然界中，由於雄果蠅會有多次交配的情形，因此OdsH的存在顯得更加重要。因此，就像OdsH一樣，雜交雄性不孕基因對於適合度具有很大的影響力，而且也是天擇所作用的對象。再者，藉由gene targeting的方法製造突變認為可用來解決OdsH和unc-4是否具有相同功能這個議題。

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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