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There still exists a remarkable difference on the yak’s taxonomic status in Bovinae.Primers designed according to the mitochondrial gene sequences of Bos taurus reported were used to amplify and sequence the yak’s cytochrome b gene,and the whole sequence of cytochrome b gene was finally obtained.Using Ovis aries as outgroup taxa,the phylogeny about the representative species of Bovinae was analyzed.Results showed that among the different species,the ratio of transition/transversion (Ts/Tv) of Cytochrome b gene was 4.9,suggesting that the mutation was not saturation.The percentage nucleotide sequence divergence between yak and Bovinae was 8.0%-8.6%,which was higher than that of yak and Bison bison.Phylogeny analysis found that Poephagus grunniens and Poephagus mutus clustered first before gathering with Bison bison,indicating higher genetic comparability than that of Bos.The results sustained the idea that Poephagus grunniens and Poephagus mutus shared one ancestor-the primitive yak.The approximate divergence time between these two species was 0.55 million years.The data also supported the viewpoint that the yak is classified into Poephagus of Bovinae,including two species of Poephagus grunniens and Poephagus mutus.