西藏牦牛mtDNA COⅢ全序列测定及系统进化关系

 【目的】探讨西藏牦牛的遗传多样性和类群间的系统进化关系，为西藏牦牛遗传资源的合理保护和利用提供理论依据。【方法】对11个西藏牦牛类群111个个体的mtDNA COⅢ的全序列进行测定，用多种生物信息学软件分析牦牛类群的遗传多样性和它们间的亲缘关系及分类。【结果】①西藏11个牦牛类群的mtDNA COⅢ全序列长度均为781 bp，基因间没有内含子，共编码260个氨基酸，启始密码子AUG(ATG)，含一个游离碱基。4种核苷酸的平均比例分别为29.2%（T）、29.4%（C）、26.1%（A）和15.2%（G），有一定的偏倚性。②发现西藏牦牛的mtDNA COⅢ共有18种单倍型，11个牦牛类群的单倍型多样性值在0.378—0.844。表明，西藏牦牛具有较丰富的mtDNA COⅢ遗传多样性。③在mtDNA COⅢ的20种氨基酸组成中，亮氨酸平均含量最多，为11.92%，赖氨酸和半胱氨酸平均含量最少，为0.77%。碱性氨基酸、酸性氨基酸、亲水性氨基酸和疏水性氨基酸的含量分别为11.15%、4.62%、29.61%和54.61%。④从mtDNA COⅢ来看，西藏11个牦牛类群可分为3大类，即帕里牦牛（PL）系、巴青牦牛（BQ）系、斯布牦牛（SB）系。【结论】西藏牦牛有丰富的遗传多样性，可分为3大类；结果支持将牦牛划分为牛亚科中一个独立属（牦牛属，Poephagus）的观点。

Sequence Analysis of mtDNA COⅢ of Tibetan Yaks

【Objective】The objective of this study was to analyze the genetic diversity and the phylogenetic relationship of different groups of Tibetan Yaks to provide a theoretical basis for protecting genetic diversity of Tibetan Yak and utilization of resources in Tibetan Yak.【Method】The mtDNA sequence of 111 individuals′ COIII from 11 groups of Tibetan Yak was determined by using the Gel Extraction Kit recycling, then the genetic diversity of Tibetan Yak, the affiliation of 11 groups of Tibetan Yak were analyzed. 【Result】 The length of 11 Tibetan Yak groups′ COIII complete sequences were all 781 bp. There were no introns between genes. These genes could encode 260 amino acids. As a start codon, AUG (ATG) had a free base. The average ratios of four nucleotides (T, C, A, G) were 29.2%, 29.4%, 26.1% and 15.2%, respectively. It showed that the base had a bias. It was found that Tibetan Yak’s mtDNA COIII showed 18 haplotypes, the index of haplotype diversity was from 0.378 to 0.844. It showed that Tibetan Yak has rich genetic diversity in mtDNA COIII. These amino acids encoded by COIII, the highest average content is Leu (11.92%), and the lowest one is Lys and Cys (0.77%). The contents of basic amino acid, acidic amino acid, hydrophilic amino acid and hydrophobic amino acid were 11.15%, 4.62%, 29.61% and 54.61%. By phyletic evdution analysis, Tibetan Yak could be divided into three categories, which are Pali (PL) line, Baqing (BQ) line and Sibu (SB) line.【Conclusion】Through cluster analysis，the Tibetan Yak has rich genetic diversity and it could be divided into three major categories. This result supports the theory that Tibetan Yak belongs to a separate genus of bovinae.