基于mtDNA COⅠ基因的西藏牦牛遗传多样性及系统进化研究

Evolution relationship and genetic diversity of Tibetan yaks inferred from mtDNA CO Ⅰ

为从分子水平上探讨西藏牦牛的序列多态性、群体遗传多样性和系统进化关系,本研究对17个西藏牦牛类群170个个体的mtDNA COⅠ全序列进行测序,用MEGA5.0、DNASP5.0等软件分析核苷酸组成、单倍型多样性和核苷酸多样性.基于Kimura-2-Parameter双参数模型,分别采用邻近法（NJ）和最大似然法（UPGMA）构建系统进化树,分析不同牦牛类群的亲缘关系和分类.结果表明：①西藏17个牦牛类群的mtDNA COⅠ全序列长度均为1 545 bp,个体间无长度差异,无内含子,起始密码子为AUG（ATG）,终止密码子为UAA（TAA）,共编码514个氨基酸.T、C、A和G4种碱基的平均含量分别为29.5％（29.3％ ～ 29.8％）、25.5％（25.2％ ～ 25.6％）、28.7％（28.6％ ～ 28.9％）和16.3％（16.2％ ～ 16.5％）; A＋T的平均含量为58.2％,存在一定的碱基偏倚性.②在17个西藏牦牛类群的170头牦牛中,共发现mtDNA COⅠ有25种单倍型,单倍型多样性值在0～0.978之间,平均单倍型多样性和核苷酸多样性值分别为0.566、0.00326,表明西藏牦牛具有较丰富的遗传多样性.③西藏牦牛mtDNA CO Ⅰ中亮氨酸平均含量最多（11.496％）,半胱氨酸平均含量最少（0.1946％）.碱性氨基酸、酸性氨基酸的含量分别为6.6171％、4.8627％;亲水性氨基酸、疏水性氨基酸分别为57.39％、42.61％.④基于mtDNA COⅠ,西藏17个牦牛类群可分为2大类,即类乌齐（LWQ）牦牛单独成一类,其它牦牛类群聚为一类.

This paper investigated the genetic diversity, clustering relationships and genetic differentiation of Tibetan yak populations and fully sequenced on mtDNA COI of 170 units which came from 17 Tibetan yak populations. MEGA5.0, DNASP5.0 and other softwares were used to analyze the nucleotide components, haplotype diversities and nucleotide diversities. The Kimura-2-Parameter model was used, NJ and UPGMA phylogenetic tree was constructed to analyze the genetic diversities, phylogenies and classifications of different groups of Yak.① The total sequences of the mtDNA CO 1 coming form 17 Tibet yak groups were 1 545 bp in length, with no gene intron. And the initiation codon was AUG （ATG）, and the finial codon was TAA, which encoded 514 amino acids. The average ratios of 4 kinds （T, C, A ,G ） ofnucleotides were respectively 29.5%（29.3%-29.8%）, 25.5%（25.2%-25.6%）, 28.7%（28.6%-28.9% and 16.3%（16.2%-16.5%）; the average content of G＋C was 41.8% and the average content of A＋T was 58.2% as well, with an obvious base bias.② The mtDNA CO Iofthe 17 Tibetan yak groups had a total number of 25 haplotypes, and the haplotype diversity values changed between in 0-0.978, while the average haplotype diversity and the nucleotide diversity values were 0.566 and 0.00326, showing that the Tibetan yak genetic diversities are so rich .③ The average content of leucine in the Tibet yak cytochrome C oxidase subunit I was most of all（11.496%）, the least average content was cysteine （0.1946%）. Contents of basic amino acids, acidic amino acids were respectively 6.6171%, 4.8627%. Hydrophilic amino acid, hydrophobic amino acids were respectively 57.39%, 42.61%.④ The clustering relationship and analysis of molecular variance also suggested that Tibetan yak could be divided into two species.