Classification of ecological types of the Chinese yak

To investigate the genetic resources and to clarify the classification status of the Chinese yak, the Maiwa yak, Jiulong yak, Datong yak, and Tianzhu White yak were intensively studied using microsatellite DNA, RAPD (random amplified polymorphic DNA), and AFLP (Amplified Fragment Length Polymorphism) DNA markers on the basis of the previous study work of the authors' on chromosomes and blood protein polymorphisms of the Chinese yak. The overall results showed that: (1) the genetic distance based on allele frequencies at the microsatellite loci between the Maiwa yak and Jiulong yak was the largest (1.506), and as expected, the two populations of the Maiwa yak had the smallest genetic distance (1.062). The four yak breeds were clustered into two groups: the first group comprised the Jiulong yak, and the second group comprised the remaining three breeds; (2) the genetic distance between the Datong yak and Tianzhu White yak was the smallest (0.0336), whereas the genetic distance between the Jiulong yak and Maiwa yak was the largest (0.0414) based on the data from the RAPD and RFLP analyses. The four yak breeds were again clustered into two groups with the Datong yak and Tianzhu White yak grouped together first, followed by the Maiwa yak; (3) analyses of the chromosomes and blood protein polymorphisms showed a similar pattern of relationship among the breeds. Therefore, it was concluded that the Chinese yak could be considered to be of two types with the Jiulong yak and Maiwa yak as their representatives, respectively. This conclusion was in accordance with the classification proposed later by professor Cai L and his colleagues, according to which the Chinese yak was classified into two types, the ‘Qinghai-Tibetan Plateau yak’ and the ‘Hengduan Mountain Alpine yak’, although this conclusion differed from the other classifications. Considering the geographic distribution, ecological factors, history and development of the Chinese yak, it was believed that this classification is reasonable.