Abstract: 【Objective】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. 【Method】 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. 【Result】 (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.

Key words: Yak, Microsatellite, Genetic diversity