Evaluating Evolutionary Divergence Of Chinese Sheep With MtDNA

The samples were collected from 6 Chinese local sheep breeds, including Mongolian sheep, Kazakstan sheep, Tibet sheep, Tong sheep, Huyang sheep and small-tailed Han sheep. The position of collected sample covered majority of distribution of Chinese sheep. Two exotic breeds , Polled Dorset and Texel, were used as comparison. Firstly, the genetic structure was scanned by PCR-RFLP and SSCP. A novel haplotype was uncovered, we called it as haplotype C, which means revealed in China. Then, the distribution of each haplotype in each breed was estimated, respectively. Finnally, we enriched this rare haplotype. D loop including all haplotypes were amplified by PCR. These PCR products were sequenced and multiple aligned. The phylogenetic tree was reconstructed respectively with Neighbour-Joint method, UPGMA and Maximal Likelihood method. The phylogenetic reticulation was reconstructed by NETWORK 4.1. Mismatch distribution and selective neutrality test was analysised in order to evaluate whether the population size of these haplotypes expanded. Some interesting conclusions were drew as following:i. A novel haplotype was revealed, which means the third maternal lineage was unveiledin Chinese native sheep. This finding would be helpful to recognize the domestication center of sheep and to evaluate the genetic distance between breeds. Moreover, the novel haplotype does not appear in two exotic breeds, that is to say, the genetic resource in Chinese sheep is more luxuriant, ii. The replacement substitutions of base pair in D loop was showed, which are transitionsonly.iii. A nonsynonymous mutation was found in ND2 in Haplotype C population, iv. Using haplotype tree, genetic relation between populations was tentatively estimated, v. Molecular marker of mitochondrial DNA showed the genetic distance betweenTongyang and other local breeds is very high, vi. The genetic relation within haplotypes was evaluated by network, the individuals inhaplotype B become two parts according to geographical distribution.vii. Mismatch distribution showed the haplotype B population had already expanded, the population size of A and C was consistent or went through multiple bottleneck effects.