有性生殖是真核生物优越于原核生物的重要特征。它使遗传与变异这一矛盾很好地达成了“对立统一”，从而加速了生物进化的进程。但它自身是如何进化形成的仍不清楚。我们已有的研究提示：处在真核生物进化早期、以贾第鞭毛虫为代表的原生动物――双滴虫类有可能是探讨这一问题的很好模型。本项目拟首先测定其两种自由生活种类（活泼锥滴虫和膨六鞭虫）的基因组，再结合贾第鞭毛虫和旋核六鞭虫（均为寄生）的已有基因组，对它们的与有性生殖相关（参与减数分裂、细胞结合等）基因即“有性生殖基因亚组”进行鉴定和系统比较分析。同时还对逆转座子这一有性生殖“指示物”和其它细胞水平的性符号”如减数分裂、细胞结合、倍性变化等进行研究，探讨：1）双滴虫类是否是处在有性生殖进化的早期原始状态，若是，则可以其为模型开展有性生殖进化的研究；2）寄生是否是导致贾第鞭毛虫有性生殖简化甚至丧失的原因，若是，则探讨该现象在基因、基因组上发生机制和规律。

Forming gametes through meiosis and then carrying out sexual reproduction is one of the important traits that contribute to the superiority of eukaryotes over prokaryotes. This mode of reproduction can reconcile the contradiction between heredity and variation very well, and thus accelerate the evolution of organisms. However, how this important mode of reproduction evolved remains unclear. There is some evidence suggesting that Diplomonads, a group of primitive unicellular protozoans with Giardia as the representative, might be able to be taken as a valuable model to study this issue. This project is going to sequence the genomes of two free-living species, Trepomonas agilis and Heximta inflate, and then combined with the available genome databases of two parasitic species, Giardia lamblia and Spironucleus salmonicida, to perform comparative genomics studies among these four diplomonads, mainly including identification and comparison of the genes taking part in sexual reproduction -- sexual reproduction genomes, among them. Simultaneously, the sexual reproduction marker, retrotransposon, and other signs of sex such as meiosis, conjugation of cells, and ploidy changes will also be investigates and compared among them. Based on the results of the studies above, two questions will be further explored: 1) whether Diplomonads are in the primitive state of sexual reproduction evolution, if this is true, the evolution of sexual reproduction genome will be further investigated by taking them as model system; 2) whether Giardia’s simplification or even loss of sexual reproduction is the consequences of parasitic reduction, if this is true, the mechanism for this will be researched at gene and genome levels.