从细胞色素b基因全序列探讨大额牛的分子系统发生

大额牛是一种半野生半家养的珍稀牛种, 有关其起源和系统地位一直存在争议。通过PCR扩增、测序等步骤共获得了11头大额牛细胞色素b(Cyt b)基因全序列(1 140 bp)。应用分析软件, 对大额牛11条Cyt b序列进行了分析, 并结合GenBank中牛属动物6个近缘种的同源序列, 以亚洲水牛(Bubalus bubalis)为外群, 分别采用邻接法(NJ)和最大简约法(MP)构建了牛属动物分子系统发育树。序列分析结果表明, 11条大额牛Cyt b序列1 140位点中, 共发现95个变异位点(占分析位点总数的8.33 %), 定义了6种单倍型, 表明大额牛群体的Cyt b基因遗传多态性比较丰富。构建的NJ和MP分子系统树均显示, 大额牛研究群体明显分为3支, 第1支与普通牛(Bos taurus)相聚, 第2支与瘤牛(Bos indicus)相聚, 第3支与印度野牛(Bos gaurus)相聚。系统发育分析表明, 大额牛很可能是印度野牛的家养型或驯化种, 我国大额牛群体可能曾受到其他牛种血缘的入侵。

Molecular phylogeny of the gayal inferred from the analysis of cytochrome b gene entire sequences

The gayal (Bos frontalis) is a very rare, semi-wild and semi-domestic bovine species. There still exist remarkable divergences on the gayal's origin and phylogenetic status. The cytochrome b (Cyt b) gene entire sequences (1,140 bp) of 11 gayals were sequenced and analyzed. Combined with other bovine Cyt b entire sequences cited in GenBank, the phylogenetic trees of genus Bos were reconstructed by neighbor-joining (NJ) and maximum parsimony (MP) methods with Bubalus bubalis as outgroup. Sequence analysis showed that, among 1,140 sites of Cyt b gene entire sequences of 11 gayals, 95 variable sites (8.33% of all sites) and 6 haplotypes were found, showing abundant genetic diversity in mitochondrial Cyt b gene of the gayals. Both NJ and MP trees demonstrated that the gayals in this study were markedly divided into three embranchments: one embranchment clustering with Bos taurus, another clustering with Bos indicus, and the third clustering with Bos gaurus. The result of phylogenetic analysis suggested that the gayal might be the domesticated form of the gaur (Bos gaurus), and a great proportion of the gayal bloodline was invaded by other bovine species.