Study On Mitochondrial DNA Diversity And Genetic Divergence Of Chinese Yak

In the study, mtDNA D-loop of yak was sequenced in 34 individuals from 5 breeds (strains) raised in China. 55 sites were polymorphic with transition, transversion and insertion/deletion. Between the transition and transversion, the frenquency of transition was higher than that of transversion. 24 haplotypes were identified,nucleotide diversity and haplotype diversity were 1.315%,0.9697 respectively. Mutations rate was different in the yak whole D-loop, and two major hypervariable regions were revealed between 13 l-500bp and 701-751 bp.The average percent value of G+C(39%) was less than that of A+T(61%),there was bias of the content of base pair.Interpopulation nucleotide divergence and net nucleotide divergence were 0.480%-2.106%,-0.094%-0.809% respectively.Dxy and Da between Maiwa yak and other four breeds was higher than that of other yaks.Average genetic distance was 0.014 among haplotypes.There was obvious genetic divergence and small gene flow(0.46-0.52) beween Maiwa yak , Tianzhu yak and Pianniu. Random genetic drift was the main factor to affect their gene flow . While Jiulong yak and other breeds had more gene flow. Tajima ' s test of selective neutrality was not signiticant (P>0.10) in the whole yak breeds,therefore it was according with neutrality mutation. In conclusion, based on mtDNA D-loop analysis, there was a quite abundance of genetic diversity of Chinese yak and the differentiation among the different strains was significant.An NJ tree was constructed to illustrate the relationships between breeds according to the consensus sequences of D-loop.The genetic distance between Jiulong yak and Pianniu was zero and they were clustered in the same branch,furthermore Maiwa yak and other breeds had less relative connection. Combining such yak haplotypes sequences with the published sequences of in GenBank comstructed the NJ tree of haplotypes. All sequences were divided into four branches,namely cluster I, II, III, IV,and All yak sequences discovered in thisstudy belonged to cluster I .Yak and wild oxen had been more closely related than that of yak and Bos indicus or Bos taurus. The reduced network was constructed according to the mutation sites of 24 haplotypes of yak in cluster I .The reduced network analysis was the same as NJ tree of haplotypes,and all yak sequences were divided into two branches.This indicated that Chinese yak might have two domestication places.