Mitogenomic Diversity and Maternal Origins of Yak (Bos Grunniens)

Background and aim: Mitochondrial genome has the characteristics of simple structure, no recombination, maternal inheritance, high conservation, fast evolution, and high copy number. It is easy to sequence, contains high resolution phylogenetic information, and exists in a wide range of taxa. Theref ore, it is widely used in the study of biological phylogeny. At present, phylogenetic studies focus mainly on D loop region, cytochrome b gene, and protein coding sequence; phylogenetic studies using the mitochondrial complete sequence are rare. Therefore, this study aimed to conduct phylogenetic experiments using the mitochondrial complete sequence and compare the results with previous findings obtained using partial sequences. Results: Complete mitochondrial sequences of five yak populations from Qinghai and Xinjiang were obtained. The haplotype diversity of the five populations were Xueduo yak (0.992 ± 0.015), Pamir yak (0.990 ± 0.014), Yushu yak (0.963 ± 0.033), Qilian yak (0.948 ± 0.036), and Huanhu yak (0.905 ± 0.048), which showed a higher haplotype diversity compared with other breeds. A total of 78 haplotypes were obtained from 111 individuals. Among these, Yushu yak, Huanhu yak, Xueduo yak, and Qilian yak all shared haplotypes, but the Pamir yak did not share haplotypes with these four populations. Phylogenetic analysis showed that yak populations were separable into three distinct branches. The analysis identified a new phylogenetic branch with both wild and domestic yaks being represented in the new branch. The 155 haplotypes were divided into 6 haplotype groups by haplotype clustering. The haplotype group had nothing to do with the morphological group of yaks, and yaks from the same population or the same ecological group were distributed in different haplotype groups. The four haplotype groups A, B, C, and D, showed a star-shaped distribution of haplotypes. The central haplotypes were widely distributed and had a high frequency Conclusions: T he genetic diversity of yaks in Qinghai was high. Both domestic and wild yaks exhibited three different mat ernal origins. Three different maternal origins existed in ancient wild yaks before domestication, with haplogroup A being the primary haplogroup associated with yak domestication.