Genetic Structure And Phylogenetic Analysis On Tibetan Mastiff Of Two Regions

Tibetan mastiff, native to Tibet Plateau, is recognized as one of the oldest and rarest dogbreeds in the world. With the “Fever of Tibetan mastiff” in1980s, massive drain of excellentTibetan mastiffs resulted in loss of germplasm resources and varietal complexity whichattracted many scholars’ attention. As precious germplasm resources and cultural heritage, thebreed resources need to be protected in time. In order to explore genetic diversity, geneticdifferentiation, population history, and phylogenetic evolution analysis from maternal andpaternal aspects, we collected blood samples of Tibetan mastiff from Gansu and Tibetanprovince and sequenced mitochondrial hypervariable region I(HVRI), Cytb gene and DBY,UTY gene fragments on the Y chromosome to find SNP sites. The results are as follows:(1) Genetic structure and phylogenetic analysis of Tibetan Mastiff based on HVRIAfter checked and edited by softwares, the effective length of total110sequences whichincluded Gansu population(n=48) and Tibetan population(n=62) was650bp. We detected1indel site and12variable sites which defined8haplotypes. The genetic distance between eachtwo haplotypes caculated by Kimura-2-Parameter was0.002-0.014, the mean genetic distancewas0.007. The haplotype diversity (Hd)、nucleotide diversity (Pi)、the average number ofnucleotide difference (K) of them were0.808,0.00603,3.917and0.794,0.00589,3.831,respectively. Analysis of molecular variance(AMOVA) indicated that the variationintrapopulation (100.06%) was bigger than interpopulation (-0.06%), the genetic variationcoefficient Fst was-0.00055. Median-joining haplotype network and phylogenetic tree basedon HVRI sequence showed that the8haplotypes form1cluster and then4sub-clusters.(2) Genetic structure and phylogenetic analysis of Tibetan Mastiff based on CytbIn the whole110sequences of Cytb(1140bp), we found no indel and8variable siteswhich defined6haplotypes. The genetic distance between each two haplotypes was0.001-0.006, the mean genetic distance was0.003. The Hd、Pi、K of Gansu population andTibetan population were0.609,0.00234,2.666and0.649,0.00230,2.621, respectively.AMOVA indicated the variation intrapopulation (99.93%%) was bigger than interpopulation(0.07%), the genetic variation coefficient Fst was0.00074. Median-joining haplotype network and phylogenetic tree based on Cytb gene showed that the6haplotypes form1cluster andthen4sub-clusters.The results of neutrality test from HVRI and Cytb aspects by Tajima’ D and Fu’Fsshowed positive value and mismatch distribution showed multimodal distribution.(3) Phylogenetic analysis of Tibetan Mastiff based on DBY and UTYThis experiment sequenced segments of Y chromosome of40male samples andpreliminarily confirmed233bp sequence of UTY gene and2278bp sequence of DBYgene.In conclusion, based on mtDNA, the Tibetan Mastiffs were single maternal origin andthen formed3-4branches gradually. In addition, based on segments of Y chromosome, theywere single paternal origin. We found the two populations had similar genetic diversity and nopopulation differentiation, which indicated they might be protected as a whole. The Tibetanmastiff populations were in the balanced phase, without the experience of recent expansion.