Origins of the Chinese Yak: Evidence from Maternal and Paternal Inheritance

It is well understood that the yak originates from China, but facts regarding origin time and evolutionary relationship with other species of Bovini, are largely disputed. Here, we have analyzed the phylogenetic relationship of eight representative species of Bovini, based on the Cytochrome b gene of mitochondrial DNA and TSPY gene of chromosome Y. We also estimated the divergence times of these different species. Results showed that the divergence time of domestic yak (Poephagus grunniens) and wild yak (Poephagus mutus) was 0.28 MYA. Considering archaeology evidence and historical records, we suggest that the domestic yak and today's wild yak shared one common ancestor, the primitive yak, 0.28 MYA. For the yak and American bison, the sequence divergence is the lowest (3.80, 0.50) and the divergence time is the latest (0.85 - 1.19 MYA), less than that between yak and cattle/zebu (8.30, 0.75 and 1.70 - 2.15 MYA). Phylogenetic analysis indicates that the yak and American bison were clustered together. Investigation of maternal inheritance (Cytochrome b) and paternal inheritance (TSPY) also proved that the genetic relationship between the yak and American bison was the closest, they evolved from one common ancestor, and their divergence time was later, during the metaphase of Pleistocene.