家猪和野猪生长激素基因遗传多样性及人工选择作用的研究
文献类型：学位论文
| 作者 | 季吟秋 |
| 学位类别 | 博士 |
| 答辩日期 | 2008-07 |
| 授予单位 | 中国科学院研究生院 |
| 授予地点 | 北京 |
| 导师 | 张亚平 |
| 关键词 | 猪 生长激素基因 驯化 |
| 其他题名 | Sequence diversity of growth hormone gene in domestic pigs and wild boars: impacts of domestication |
| 学位专业 | 动物学 |
| 中文摘要 | 根据家养化的经典定义，由于奠基者效应和人工定向选择的作用，家养物种与其野生祖先相比遗传多样性会有明显的下降，这种现象被看做是家养化的重要特征并且在农作物中已经得到证实。但是在家养动物中我们对此还知之甚少，推究其原因这主要是由于现有数据的稀少和家养动物野生祖先样本的匮乏造成的。野猪，作为家猪的野生祖先，是当前家养动物野生祖先中唯一现存种群繁盛的物种。家猪与野猪在世界上的广泛分布，为了解家养化对家养动物基因多样性的影响提供了良好的机会。 本文选择猪生长激素（pGH）基因为研究对象，采用PCR、克隆、测序的方法获得了690条欧亚猪的pGH基因全序列，鉴定了124个多态位点和117种单倍型，此外我们还测定了马来亚野猪、非洲疣猪和红河猪的序列作为外群进行系统发育关系的分析。结果显示无论在野猪还是在家猪中，pGH基因都没有明显的系统地理结构，并且作为外群的马来亚野猪与欧亚猪之间的遗传分化不明显，这一结果与mtDNA所显示的野猪和家猪具有明显的系统地理结构不一致，这提示pGH基因具有高度的保守性，与mtDNA D-loop区相比进化缓慢，因此无法像mtDNA那样能够在不同地理区域之间产生遗传分化从而具有显著的系统发育地理结构，因此pGH基因数据对探讨家猪起源的信息不足。 为了了解家养化过程中的奠基者效应和人工选择作用对家养动物遗传多样性产生的影响，我们对pGH基因进行了群体遗传学方面的分析，同时还参考了其他工作中的数据——mtDNA D-loop区和GPIP假基因的数据对野猪和家猪的遗传多样性进行了综合比较。结果显示pGH基因在家猪中的遗传多样性并不比野猪的低，这与mtDNA D-loop区和GPIP假基因的数据所显示的家猪与野猪相比遗传多样性有明显下降的结果不一致，由于pGH基因被证实与一些经济性状有显著相关，很可能受到人工选择的作用，因此我们推测该基因在家猪中高的遗传多样性可能是由人工选择造成的。对pGH基因进行中性检验的结果揭示了该基因受到的自然选择作用是纯化/负选择，而在家猪中受到的人工选择作用是定向选择。为了阐明pGH基因在家猪中受到的人工选择作用和遗传多样性之间的关联，我们对该基因在家猪和野猪中的单倍型频率分布进行了比较分析，结果显示家猪与野猪相比其单倍型频率分布有由低向高发展的趋势，这提示了该基因在家猪中受到的人工选择作用可能是由多个定向选择构成，从综合效应看等同于平衡选择，这种选择作用通过提升多个等位基因的频率提高并维持了该基因在家猪中较高的遗传多样性。虽然pGH基因在家猪中的遗传多样性水平与野猪相比没有下降，但是来自其他方面的证据如低频率等位基因的丢失、等位基因频谱的改变以及LD的提升等都显示了奠基者效应的确存在，此外来自mtDNA和GPIP假基因的中性分子标记的数据揭示了之前所说的家养化特征仍然是适用于家养动物的线粒体基因组和核基因组的。 |
| 英文摘要 | Based on the classical definition of domestication, loss of genetic diversity in domesticated species relative to their wild ancestors would be expected ascribed to founder effects and artificial selection, which is seen as a common feature of domestication and has been proved in crops. However, our understanding of this feature in livestock is very limited because of the scarcity of existing data and the lack of the wild ancestor samples. Wild boar, the ancestor of domestic pig, is widely distributed in the world, which affords us an excellent chance to study the impacts of domestication on livestock genetic diversity. We chose growth hormone gene as study object, obtained totally 690 pGH gene sequences from 115 wild boars and 230 domestic pigs by PCR, cloning and sequencing, and identified 124 nucleotide polymorphisms, which defined 117 distinct haplotypes. Moreover, the sequences of Malaya wild boars, warthog and red river hog were obtained to be used as outgroups in phylogeny analysis. The results showed that in both domestic pigs and wild boars, pGH gene did not show a significant phylogeographic structure consistent to that of mtDNA, and there was no obvious differentiation between Malaya wild boars and Eurasian pigs. This suggests that pGH gene was highly conserved and evolved more slowly than mtDNA, so it could not behave like mtDNA to produce genetic differentiation among the different geographical subpopulations and to have a significant phylogeographic structure. As a result, pGH gene is unable to be used to study the origin of domestic pig just like mtDNA. To understand the impacts of founder effects and artificial selection on livestock genomes during domestication, we performed population genetic analyses on pGH gene and borrowed the data of mtDNA D-loop and GPIP from other works in our lab to compare synthetically the genetic diversity between wild boars and domestic pigs. The results showed that there was no significant reduction in the genetic diversity of pGH gene in domestic pig relative to wild boar, which was different from the results of mtDNA D-loop and GPIP. Since pGH gene was proved to be associated with some economic traits and might be acted by artificial selection, we presumed that the high genetic level of this gene in domestic pigs should be formed by artificial selection. The results of neutrality tests suggested that natural selection acting on pGH gene should be purifying/negative selection and artificial selection acting on this gene should be positive directional selection. To elucidate the connection between genetic diversity and artificial selection on pGH gene, we analyzed and compared the haplotype frequency spectrums of this gene between wild boars and domestic pigs. The results showed that there was a slight increase in the proportion of haplotypes with relatively high frequency in domestic pig relative to wild boar, which implied that artificial selection acting on this gene was composed by several positive directional selections. From the synthetical effects, this situation was very similar to that of balancing selection. And whether as several directional selections or synthetically as balancing selection, artificial selection is the main force to preserve the genetic level of domestic pig at the pGH locus by increasing the frequencies of multiple favored alleles. Although there was no reduction of genetic diversity at pGH in domestic pigs, there were other evidences such as the loss of low-frequency alleles, the change of the allele frequency spectrum and the increase of LD to support the existence of founder effects on this locus. Moreover, the data of neutral markers (mtDNA D-loop and GPIP) indicated that the above mentioned feature of domestication should also be fit to mtDNA genomes and nuclear genomes of livestock like crops. |
| 语种 | 中文 |
| 公开日期 | 2013-04-22 |
| 源URL | [http://159.226.149.42:8088/handle/152453/7359]  |
| 专题 | 昆明动物研究所_分子进化基因组学 |
| 推荐引用方式 GB/T 7714 | 季吟秋. 家猪和野猪生长激素基因遗传多样性及人工选择作用的研究[D]. 北京. 中国科学院研究生院. 2008. |
入库方式： OAI收割
来源：昆明动物研究所
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