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The present day structure of the vertebrate major histocompatibility complex (MHC) and its three paralogous regions has always been a focus of interest. In a recent study, nine human anchor genes located in the MHC region were cloned from a Branchiostoma floridae (amphioxus) cosmid library. The identification and analysis of 31 surrounding genes led to the most probable model of two rounds of en bloc duplication giving rise to these regions. These events were estimated to have occurred after the cephalochordata-craniata divergence [approximately 766 million years ago (Mya)] and before the Gnathostomata radiation (approximately 528 Mya). Furthermore, it was also shown that after this large-scale duplication one of these regions, corresponding to the human 9q33-q34, had retained an ancestral organisation. In the present study, four new cosmids in the amphioxus proto-MHC region were identified by the chromosomal walking technique. These cosmids were sequenced, and their structural annotation was performed, leading to the prediction of eleven genes. Their phylogenetic relationships among species corroborate the results obtained previously and provide more evidence for the plesiomorphic state of the human chromosome 9q33-34 MHC paralogous region.An erratum to this article can be found at  相似文献   
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似鮈类鱼类的系统发育研究(鲤形目:鲤科)   总被引:1,自引:0,他引:1  
本文通过对似类8属13种和外类群7属10种鱼类的比较研究,选取37个骨骼及外部特征,运用外类群比较法进行特征分析,根据分支系统学原理重建了似类的系统发育。特征分析和系统发育分析表明似类是具有许多共同离征的单系群,朝着流水性底栖生活和刮食性的主干方向发展;其中以似属最原始,胡属最特化构成7对姐妹群。蛇属是较早分化出的相对特化的类群,棒花鱼属和小鳔属的关系相对较远。  相似文献   
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匡溥人 《动物学研究》1993,14(4):299-306
错头鳋科Lernaeidae是剑水蚤目Cyclopoida中以第1触短和第1小颚单枝型或退化消失为共同离征的一个自然类群,因此以剑水蚤科Cyclopidae作为外群,把锚头鳋科各属筛选出的性状与剑水蚤科的相应性状比较,以确定其性质,即该性状为祖征,还是离征。经比较,发现21个性状在锚头鳋科11个属中呈镶嵌分布。根据性状的镶嵌分布和简约性原则,推导出锚头鳋科的属间系统发育分支图。  相似文献   
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