本研究利用已公布的4165个来自于全世界196个品种的山羊线粒体D_Loop序列，进行核苷酸多样性、单倍型构建、单倍型多样性、群体系统发育学研究、中性检验及群体遗传距离等一系列遗传参数进行评估。在全部个体的401 bp片段长度的D_Loop区域内共鉴定得到301个多态位点，总体核苷酸多样性为0.03471；构建获得并构建2409个D_Loop单倍型，单倍型平均多样性为0.9983。系统发育分析表明，98.92%的单倍型被聚类为已知的6个山羊线粒体D_loop单倍型簇，其中单倍型A所占比例最大(86%)，D_Loop单倍型B簇在中国山羊中出现频率最高。中国西南地区山羊群体中发现了两个未知的D_Loop单倍型簇(Unknown I和Unknown II)。分子方差分析(AMOVA)和群体间成对差异(PiXY)研究结果表明，不同品种家养山羊间群体变异较小，群体遗传分化与地理分布不完全一致，表明群体间广泛存在遗传物质交流。中性检验(Tajima‘D和Fu’Fs检验)和错配分布研究结果表明，单倍型簇B、C和G存在群体扩张历史。较其他野羊，Capra aegagrus与家养山羊系统发育关系最为密切，并可能贡献于山羊A、B、C和F单倍群簇的驯化起源。本研究表明线粒体D_Loop单倍型B簇可能起源于中国或在山羊驯化早期已迁至中国，在中国西南地区山羊群体中两个未知的D_Loop单倍型簇的发现表明中国西南地区可能具有独特的山羊母系背景或驯化历史；Capra aegagrus是最可能的家养山羊野生祖先，并可能贡献于山羊A、B、C和F单倍群簇的驯化起源。本研究利用大样本量全世界山羊线粒体D_Loop序列数据集分析有助于更好的理解世界范围内山羊母系驯化起源及基因流动的历史变化，为进一步明确世界山羊群体迁徙的演变历史及种群系统发育定位提供了宝贵的理论依据。

Received  24 October, 2017    Accepted  29 January, 2018

Endothelial PAS domain protein 1 (EPAS1), also called hypoxia-inducible factor-2, is a key regulatory factor of hypoxic responses and plays an essential role in high-altitude adaptation in mammalian species. In this study, polymorphisms of EPAS1 were detected in 217 individuals from 2 Tibetan pig populations and 3 low-altitude pig breeds by DNA pooling, PCR-SSCP, PCR-RFLP and DNA sequencing methods. A total of 14 synonymous polymorphisms were identified in the coding region. The analysis suggested that SNP1 (G963A), SNP7 (C1632T), SNP10 (G1929A) and SNP11 (G1947A) showed potential association with high-altitude environment because of their particular variation patterns in Tibetan pigs. Linkage disequilibrium (LD) of these SNPs was analyzed. One common LD block including 5 SNPs clustering in exon 12 was identified in all studied pig populations. Haplotype H1 (AGGTC) in LD block was dominant in Tibetan pigs (76.6 and 74.2% in Linzhi (LZ) and Chayu (CY) pigs, respectively) and segregated at higher frequency than that in low-altitude pig breeds (52.3, 58.7 and 56.2% in Wuzhishan (WZS), Min (M) and Laiwu (LW) pigs, respectively), indicating that H1 may relate to adaptation to high altitude in Tibetan pigs. These findings raise hope that EPAS1 gene can be a candidate gene that involved in adaptation of high altitude in Tibetan pigs.