Abstract:

This study explored the genetic diversity， phylogenetic evolution， and genetic relationship between Pali yak， Jiali yak， Leiwuqi yak， Gongbujiangda yak， Sibu yak， Sangri yak and Jiangda yak. Coding sequences （CDS） of the mitochondrially-encoded cytochrome c oxidase subunit Ⅲ gene （COX3） were determined in 140 individuals from seven groups of Tibetan yak by PCR and direct sequencing. DNAMAN， DNASP 5.1， and MEGA 7.0 software programs were used to analyze COX3 polymorphisms and haploid diversity， and a phylogenetic tree was constructed. The COX3 CDS sequence was shown to be 781 bp in all seven Tibetan yak groups， with 55 sites of variation. Tibetan yak COX3 showed 11 haplotypes and average haplotype diversity （H_d） and nucleotide diversity （P_i） levels of 0.665 and 0.00480， respectively， indicating a rich genetic diversity. Phyletic evolution analysis constructed a network relationship chart dividing the 11 haplotypes into two clusters， suggesting that the Tibetan yak can be categorized as the Leiwuqi yak line and a second yak line. Thus， Tibetan yaks may be descended from two separate maternal lineages. They can also be divided into three haplotype groups： domestic yak （Bos grunniens）， Bos primigenius， and Bos taurus. Hap_2， Hap_3， Hap_4， Hap_6， Hap_7， Hap_8， Hap_10， and Hap_11 belong to the Bos grunniens line， Hap_5 and Hap_9 to B. primigenius and B. taurus lines， and Hap_1 to the Bos mutus line. Although Tibetan yak have mixed matrilineal origins， they appear to be greatly influenced by domestic yak. These findings provide a theoretical basis for understanding the evolution of Tibetan yak， and in planning their conservation and utilization of genetic resources.

Key words: Tibetan yak, COX3 gene, genetic diversity, system evolution