Genetic Structure And Maternal Origins Of Ten Tibetan Goat Populations Inferred From Mitochondrial DNA D-loop Sequences

Tibetan goats are mainly distributed in the Qinghai-Tibetan Plateau,where the average altitude is 4 000m.Dramatically different topographical environment,ecological conditions,with long-term manual selection and natural selection,could have produced unique genetic resources of Tibetan goats.China has abundant Tibetan goat populations,whereas the genetic structure and maternal origin of different Tibetan goat groups remain uncertain.Mitochondrial DNA?mtDNA?D-loop,which is the fastest evolved and the most polymorphic region,has been used to study phylogeny and genetic diversity of species.Here,to disclose the information of genetic structure and maternal origins of Tibetan goats,111 mitochondrial D-loop sequences of individuals from 8 Tibetan goat populations located in distinct plateau areas,were amplified and sequenced.Nineteen additional D-loop sequences were obtained from two additional Tibetan goat populations?Sichuan-Aba and Jiangzi County?were downloaded from NCBI.Finally,the genetic diversity,genetic differentiation index,and phylogenetic tree were analyzed.Main results are as follows.1.The length of D-loop was 1 211¹ 213bp,and 164 variation sites were detected among the 130 sequences.There had been two insertions or deletions?277bp and 1 075bp?.86haplotypes were defined,among which 97.7%?84/86?were group-specific haplotypes.Haplotype diversity?Hd?and nucleotide diversity?Pi?indices for Tibetan goats were 0.990and 0.0145 respectively,indicating that Tibetan goats have rich genetic diversity.However,genetic diversity of the Chengguan goats were low?Hd=0.33±0.215,Pi=0.0045±0.0029?.2.57.8%of Pairwise Wright's F-statistics(F_ST)indices was significant differentiation?26/45?,and 68.9%?31/45?were greater than 0.05 among the populations.AMOVA analysis(F_ST=0.0858,P<0.001)revealed that 8.58%of the total genetic variation was attributed to external populations,suggesting that the genetic structure of Tibetan goats had been weaker.3.Phylogenetic trees revealed that the Tibetan goats were divided into four haplogroups?A,B,C,and D?,of which haplogroup A was predominant,suggesting that Tibetan goats had4 maternal origins.Network of haplotypes showed that there was no association between population clustering and sample location.4.Additionally,the complete dataset of neutrality tests?Fs=-33.67,P<0.01?was a significantly negative value,and mismatch distribution analyses indicated that at least one population expansion event occurred during the demographic history of Tibetan goat.Consequently,these results demonstrated that Tibetan goats in china have rich genetic diversity,and the breed has 4 multiple origins.Although apparent genetic differentiation has been occurred among the populations,there is no strong phylogeographic structure.And the genetic structure has become weak.These results will provide a scientific basis for protecting the genetic resources of Tibetan goats.