Abstract: 328 individuals from 8 Tibetan yak populations (i. e. Riduo,Leiwuqi,Dingqing,Cuona,Longzi,Zhongba, Nierong and Shenzha)were analyzed by means of PCR amplification and sequence analysis of mitochondrial DNA control region (mtDNA D-loop)to explore the level of genetic diversity within populations and phyletic evolution between individuals. DnaSP4. 0 was used to compute genetic diversities within populations. MEGA5. 0,MrBayes3. 2 and PhyML3. 0 were
used to analyze phyletic evolution between individuals. Results showed that the length of the nucleotide sequence was from 887 bp to 895 bp,and a total of 91 haplotypes were identified with 135 polymorphic sites including 52 single nucleotide polymorphisms sites and 83 parsimony-informative sites. Nucleotide mutation types included deletions,insertions,transitions and transversions. The average haploid type diversity and nucleotide diversity were 0.884 and 0. 010 27,respectively, indicating a high level of genetic diversity in Tibetan yak populations. The genetic distance between Riduo and Cuona
was the least (0. 006),while genetic distance between Leiwuqi and Longzi was the largest (0.015). ML and BI phylogenetic tree showed that Tibetan yak populations could be divided into two major groupes. In brief,Tibetan yaks have abundant genetic diversity. Meanwhile,the Tibetan yak populations could be divided into two major groupes. Cuona yaks can be used as a truebred population to save and utilize. Other populations once communicated with each other in the course of evolution.

Key words: D-loop region of mitochondrial DNA, Genetic diversity, Phyletic evolution, Tibetan yak

摘要： 为从分子水平上探究西藏牦牛类群的遗传多样性、亲缘关系,本研究测定了日多牦牛、类乌齐牦牛、丁青牦牛、错那牦牛、隆子牦牛、仲巴牦牛、聂荣牦牛、申札牦牛等8 个西藏牦牛类群共328 头牦牛mtDNAD-loop区序列,分析其多态性,构建系统进化树。结果表明:本次测定的西藏牦牛mtDNA D-loop 区序列长度为
887 - 895 bp,共检测到135 个变异位点,其中单态突变位点52 个,简约信息位点83 个。在328 个个体中共检测出91 种单倍型,平均单倍型多样性(Hd)、平均核苷酸多样性(π)分别为0. 884、0.010 27,显示西藏牦牛具有丰富的遗传多样性。8 个类群间平均遗传距离为0.011;日多牦牛与错那牦牛间遗传距离最小(0. 006);类乌
齐牦牛与隆子牦牛间遗传距离最大(0.015)。系统进化分析显示西藏牦牛可分为两大类,错那牦牛是较纯的牦牛类群,其它牦牛类群在进化过程中出现相互交流的情况。

关键词: 西藏牦牛, mtDNA D-loop 区, 遗传多样性, 系统进化