家犬作为人类最亲密的朋友，在人类历史上一直扮演者重要的作用。更重要的是，家犬是人类最早驯化的家养动物，由于其经过了驯化和品种培育两个重要的群体历史阶段，并且在家养哺乳动物中形成了最具多样性的品种，因此家犬一直是研究人工选择和自然选择的重要模式生物。中国最为家犬的驯化地，不仅遗传多样性最为丰富，而且由于其庞大的乡村狗种群数量，为研究家犬提供了最为丰富的材料。在家犬和人类的共同历史中，嗅觉发挥了极其重要的作用，研究家犬的嗅觉受体基因很有意义。
在导师张亚平院士的指导下，中科院昆明动物研究所博士生陈睿对家犬嗅觉受体基因家族中的分离假基因，在狼及中国土狗以及已经发表的品种犬的数据进行分析。在各自特有的多态性位点中，品种犬中存在着很强的负选择，而狼和中国土狗近乎中性。但是，通过对非同义位点的进一步的细分，研究发现狼中的嗅觉受体基因在积累着无害突变，去除有害突变，而嗅觉受体在中国土狗中近乎中性。随后，研究人员通过对多态性位点在七次跨膜结构上分布的分析，进一步验证了这个结论，并且对各个群体特有多态性及共有多态性的分析，发现选择作用在祖先群体及狼的嗅觉受体基因中精细微妙，而其在品种犬中就未有这种效果。
研究结果不仅显示了在家犬两次重要历史阶段后，家犬的嗅觉受体基因所受的选择作用发生了两次深刻的变化，而且展示了自然选择和人工选择的不同，为以后的品种培育及改良提供了借鉴。
该工作近期在Molecular Biology and Evolution杂志在线发表。（生物谷Bioon.com）
doi:10.1093/molbev/mss153
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Differences in selection drive olfactory receptor genes in different directions in dogs and wolf
Rui Chen1,2, David M Irwin1,3 and Ya-Ping Zhang1,4
The olfactory receptor (OR) gene family is the largest gene family found in mammalian genomes. The OR gene family is known to evolve through a birth-and-death process. Here we characterized the sequences of 16 segregating OR pseudogenes in samples of the wolf and the Chinese village dog (CVD), and compared them with the sequences from dogs of different breeds. Our results show that the segregating OR pseudogenes in breed dogs are under strong purifying selection, while evolving neutrally in the CVD, and show a more complicated pattern in the wolf. In the wolf we found a trend to remove deleterious polymorphisms and accumulate non-deleterious polymorphisms. Based on the protein structure of the ORs, we found that the distribution of different types of polymorphisms (synonymous, nonsynonymous, tolerated and untolerated) varied greatly between the wolf and the breed dogs. In summary, our results suggest that different forms of selection have acted on the segregating OR pseudogenes in the CVD since domestication, breed dogs after breed formation, and in the ancestral wolf population, that has driven the evolution of these genes in different directions.
