Evolutionary Origin and Genetic Differentiation of Dopamine Receptor D2, D3 and D4 Genes of Japanese Domesticated Chickens

在本研究中，我们的主要目的是通过分析多巴胺受体基因(DRD2、DRD3和DRD4)的基因变异与物种之间的关系，进一步了解家鸡的祖先和驯化过程。此外，我们试图澄清攻击性与过去人类人工选择鸡之间的关系。为了实现这一目标，我们对日本家鸡的3个品种(斗鸡、长冠和观赏鸡)的DRD2、DRD3和DRD4基因进行了进化分析和遗传分化研究，共分析了8200个碱基对，从这些结果中，我们发现了不同的核苷酸频率和多态类型，可以作为每个家鸡种的标记。此外，我们还能够证明，为了培育现代观赏鸡的新品种，对祖先的斗鸡种群进行了密集的人工选择，这导致了我们今天所知的具有深刻差异的日本家鸡。

In the present study, our primary goal was to further understand the ancestry and domestication processes of domesticated chickens by analyzing the relationship among gene variations of dopamine receptor genes(DRD2, DRD3, and DRD4) and species. In addition, we sought to clarify the relationship between aggressiveness and past artificial selection of chickens by humans. To accomplish this goal, we performed an evolutionary analysis and studied the genetic differentiation of DRD2, DRD3 and DRD4 genes for three varieties of Japanese domesticated chickens(fighting cock, long-crowing, and ornamental), analyzing a total of 8, 200 base pairs.From these results, we found different nucleotide frequencies and polymorphism types that might be used as markers for each domesticated chicken species. Furthermore, we were able to show that in order to breed the novel varieties of present day ornamental chickens, intensive artificial selection was forced upon ancestral fighting cock populations, which resulted in the profoundly differentiated Japanese domesticated chickens we know today.