1 INTRODUCTION
Yak (Bos grunniens ), known as the ”boat of the plateau”, is a vulnerable bovine species endemic to the Qinghai-Tibet Plateau (QTP) with an altitude of 2,000~6,000m above sea level (Qiu et al., 2012; Wang et al., 2011). At present, there are more than 15 million wild and domestic individuals worldwide, but about 95% of which are lived in China (Wiener et al., 2003). Qinghai Province of China owns abundant yak genetic resources. It possessed four officially recognized indigenous breeds (Qinghai-Gaoyuan, Huanhu, Xueduo, Yushu) and two improved breeds (Datong and Ashdan). Mitochondrial DNA (mtDNA) owns the characteristics of maternal inheritance and high variation rate, that making it as an important molecular marker to explore the evolution history, origin and genetic diversity of mammals (Bruford et al., 2003; Lunkina et al., 2004; Srivastava et al., 2015; Maltsev et al., 2015). The mammalian cytochrome b gene (Cytb ), located in the functional region of mitogenome, is a mitochondrial oxidative phosphorylation complex protein encoding 379 amino acids (Hatefi, 2018). Compared with the mtDNA D-Loop region, Cytb is more conserved and also has been widely used in the studies on animal’s population genetics in recent years. Previously, some studies analyzed mtDNA D-loop region to explore the maternal genetic diversity of wild yak and Qinghai domestic yak populations (Ma et al., 2010; Wang et al., 2010), but relatively few studies are done based on Cytbvariations. Again, to date, most Cytb studies conducted have focused explicitly on a few Chinese yak populations (e.g. Bazhou, Jiali, Sangsang, Sangri, Gongbujiangda, Sibu, Pali, Kangbu, Jiangda, Leiwuqi, Dingqing, Baqing, Zhongdian, Taxkorgan, Karakorum-Pamir, Shenzha, and wild yak) (Yang et al., 2009; Chang et al., 2010; Ji et al., 2012; Wang et al., 2013; Tu et al., 2016; Hu et al., 2018; Liu et al., 2019; Li et al., 2019; Ji et al., 2019; Wang et al., 2021), but which were limited to four domestic yak breeds in Qinghai Province of China (Wang et al., 2021).
In this study, we comprehensively analyzed maternal genetic diversity and differentiation of six wild and domestic yak breeds/populations (wild, Qinghai-Gaoyuan, Huanhu, Xueduo, and Yushu yak) in Qinghai, and explored their clustering relationship and phylogeny based onCytb sequence variations so as to provide baseline information for the conservation and utilization of these valuable yak genetic resource.