Study on genetic diversity and classification of the yak

صينى. 对中国部分牦牛品种即麦洼牦牛、九龙牦牛、大通牦牛、天祝白牦牛的遗传多样性及其分类进行研究，从而揭示其遗传多样性程度和进行较为合理的类型划分。用9个微卫星标记对上述牦牛品种的等位基因频率、多态信息含量、杂合度和有效等位基因数等指标进行统计分析，并在此基础上对其进行合理的聚类分析和分类研究。（1）9个微卫星标记在所检测的牦牛群体中都表现出较丰富的多态性，均为高度多态位点。每个微卫星标记平均检测到6.8个等位基因（5～9）；9个微卫星标记的平均多态信息含量（PIC）为0.6534（0.5037～0.7351），各群体的平均多态信息含量（PIC）差异不显著；全部群体平均杂合度为0.6625，麦洼牦牛（若尔盖群体）平均杂合度最高，为0.6883，而九龙牦牛杂合度最低，为0.6317；各群体平均有效等位基因数为3.2680（3.189～3.4478），其中九龙牦牛最少。这显示牦牛群体的等位基因频率、多态信息含量、杂合度和有效等位基因数等指标有较好的一致性，说明牦牛品种间和品种内在微卫星位点上均具有丰富的遗传多样性。（2）通过各指标的分析可以看出，九龙牦牛与其它牦牛品种的差异比较大，遗传距离和聚类分析结果也表明了这一差异。在遗传距离中九龙牦牛和麦洼牦牛（红原群体）的遗传距离最大，为1.506；麦洼牦牛两个群体之间的遗传距离最小，为1.062。5个牦牛群体被聚为两大类，九龙牦牛单独成一大类，其他牦牛品种聚为一类。麦洼牦牛的两个群体在较近的水平上首先聚在一起，大通牦牛和天祝白牦牛在稍远的距离处聚在一起。该聚类结果与各牦牛品种的地理分布、所处生态条件、育成史及其分化的实际情况是一致的,也同蔡立等的分类结果相同。（1）中国牦牛品种间和品种内在微卫星位点上均具有丰富的遗传多样性；（2）本研究中的5个牦牛群体聚为两大类，与蔡立等将中国牦牛划分为横断高山型和青藏高原型的结果基本一致，说明中国牦牛分为两个类型是合理的。

إنجليزي. The genetic diversity and classification of partial chinese yak breeds including Maiwa yak (two populations), Jiulong yak, Datong yak, and Tianzhu white yak were studied in order to indicate the degree of genetic diversity and provide a more reasonable type division. The genetic diversity of nine microsatellite sites in above five yak populations was studied by means of PCR, and the alleles frequency, polymorphism information content (PIC), heterozygosity (H) and effective number of alleles(Ne) in different yak populations computed by means of statistics method. At the same time, the cluster of these yaks has also been researched. (1) The nine microsatellite sites analyzed were polymorphic in these yak populations and all of them were highly polymorphic sites. The average numbers of alleles and polymorphism information content (PIC) in each site were 6.8 (ranged from 5 to 9) and 0.6534 (from 0.5037 to 0.7351) respectively. The difference of average PIC among these populations was not significant. The average heterozygosity in all populations was 0.6625, which varied from the highest in Ruoergai population of Maiwa yak (0.6883) to the lowest in Jiulong yak (0.6317). Accordingly, the average effective number of alleles was 3.2680(ranged from 3.189 to 3.4478), with the lowest for Jiulong yak. These results indicated that there was a good compatibility between the parameters including allele frequencies, PIC, heterozygosity(H) and effective number of alleles(Ne) in different yak populations. It also showed that there was rich in genetic polymorphisms of microsatellite sites within a breed and between breeds of the yak. (2) All calculated parameters showed that there was a significant difference between Jiulong yak and other yak populations. The same conclusion could be also taken from the results of genetic distance and cluster analysis. The greatest genetic distance (1.506) occurred between Jiulong yak and Maiwa yak of Hongyuan, while the lowest (1.062) occurred between two populations of Maiwa yak. These five yak populations could be classified as two groups by clustering analysis, i.e., Jiulong yak was a separate group, the other four populations were in another. The two populations of Maiwa yak were clustered as one at first, then the Datong Yak and the Tianzhu white yak. This result was in accordance with the fact of their distribution, ecological conditions, the breeding history and differentiation of different yak populations, and it was also as same as classification result of Cai Li.【Conclusion】(1) There was rich in genetic polymorphisms of microsatellite sites within a breed and between breeds of the chinese yaks. (2) This cluster result was in accordance with the classification of Cai Li. So, it was reasonable to classified Chinese yaks into two types including Qinghai-Tibetan Plateau yak and Henduan mountain Alpine yak.