Sequence Analysis of mtDNA COIII of Tibetan Yaks

【Objective】The objective of this study was to analyze the genetic diversity and the phylogenetic relationship of different groups of Tibetan Yaks to provide a theoretical basis for protecting genetic diversity of Tibetan Yak and utilization of resources in Tibetan Yak.【Method】The mtDNA sequence of 111 individuals′ COIII from 11 groups of Tibetan Yak was determined by using the Gel Extraction Kit recycling,then the genetic diversity of Tibetan Yak,the affiliation of 11 groups of Tibetan Yak were analyzed.【Result】 The length of 11 Tibetan Yak groups′ COIII complete sequences were all 781 bp.There were no introns between genes.These genes could encode 260 amino acids.As a start codon,AUG(ATG) had a free base.The average ratios of four nucleotides(T,C,A,G) were 29.2%,29.4%,26.1% and 15.2%,respectively.It showed that the base had a bias.It was found that Tibetan Yak's mtDNA COIII showed 18 haplotypes,the index of haplotype diversity was from 0.378 to 0.844.It showed that Tibetan Yak has rich genetic diversity in mtDNA COIII.These amino acids encoded by COIII,the highest average content is Leu(11.92%),and the lowest one is Lys and Cys(0.77%).The contents of basic amino acid,acidic amino acid,hydrophilic amino acid and hydrophobic amino acid were 11.15%,4.62%,29.61% and 54.61%.By phyletic evdution analysis,Tibetan Yak could be divided into three categories,which are Pali(PL) line,Baqing(BQ) line and Sibu(SB) line.【Conclusion】Through cluster analysis,the Tibetan Yak has rich genetic diversity and it could be divided into three major categories.This result supports the theory that Tibetan Yak belongs to a separate genus of bovinae.