中文摘要：

【目的】研究牦牛和犏牛Dmc1基因编码区序列、结构和睾丸组织mRNA表达水平,探讨Dmc1基因与犏牛雄性不育的关系,为揭示犏牛雄性不育的分子机理提供参考。【方法】通过PCR扩增和克隆测序获得牦牛和犏牛Dmc1基因部分cDNA序列,运用生物信息学方法分析牦牛和犏牛Dmc1基因编码区序列、蛋白结构和进化关系,利用实时荧光定量PCR技术检测牦牛和犏牛睾丸组织中Dmc1基因mRNA表达水平。【结果】牦牛和犏牛Dmc1基因编码区序列全长均为1023bp,编码340个氨基酸,与黄牛Dmc1基因的同源性为100%,与哺乳纲其它物种的同源性在90%以上。牦牛和犏牛Dmc1蛋白含有RecA蛋白家族典型的第二结构域,且与人、鼠Dmc1蛋白结构域一致。系统发育分析显示牦牛、犏牛和黄牛首先聚为一类,后与家犬相聚;人、黑猩猩和猕猴聚为另一类,而与鸟纲动物相聚较远,与经典分类基本一致。定量结果显示犏牛睾丸组织Dmc1基因mRNA表达水平较低,与牦牛差异极显著（P〈0.01）,且犏牛表现出来的减数分裂障碍表型与小鼠Dmc1基因突变或敲除的表型一致。【结论】根据生物信息学分析结果推测牛Dmc1蛋白与人、鼠一样,在精母细胞减数分裂同源重组过程中发挥着重要作用;Dmc1基因在牦牛和犏牛睾丸组织中的表达量差异极显著（P〈0.01）,结合犏牛雄性减数分裂障碍表型,表明睾丸组织Dmc1基因可能与犏牛的雄性不育有一定的关系。

英文摘要：

【Objective】 The study was aimed to investigate the coding region sequences, their structures and the expression levels of Dmc1 mRNA in yak and cattle-yak testis, so as to offer references for the revealing of the molecular mechanism of infertility of cattle-yak.【Method】RT-PCR was applied to clone the cDNA of Dmc1 gene. The coding region sequences, protein structures and phylogenetic relationships were analyzed by bioinformatics software. Real-time PCR was employed to examine the expression levels of Dmc1 mRNA in yak and cattle-yak testis. 【Result】 The coding region sequences of Dmc1 gene in yak and cattle-yak, had 1 023 bp in length, encoded 340 amino acid residues and showed 100% sequence identity with cattle and above 90% with other mammals. Both yak and cattle-yak’s Dmc1 protein contained the domain II region, which was highly conserved in the E.coli RecA-like protein family, and had the same domain regions as other mammalian Dmc1 proteins. Phylogenetic analysis showed that the cattle, yak and cattle-yak were in the same clustering, and then clustered with canine lupus familiaris, and that human, pan paniscus and macaca mulatta were in another clustering, both of which had a distant relationship with Gallus gallus. Real-time PCR analysis indicated that the difference of expression level of Dmc1 mRNA between yak and cattle-yak was extremely remarkable （P〈0.01）, and both the Dmc1 mutant and Dmc1-knockout between cattle-yak and mice showed close similarity in phenotypes. 【Conclusion】 It was dedued that Dmc1 protein in cattle might play a key role in meiotic recombination, as which in human and mice. Dmc1 mRNA represented a dramatic difference in expression level between yak and cattle-yak, and the low expression in cattle-yak testis may be related to maleinfertility of cattle-yak, thus reflecting that Dmc1 might be a candidate gene in male infertility of cattle-yak.