Phylogenetic analysis of some metazoans based on new molecular marker, mitochondrial gene arrangements.

后生动物线粒体DNA（mtDNA）是一个约16 kbp的闭合环状分子。这个小基因组通常编码37个基因。虽然线粒体基因排列通常是保守的，但基因组重排偶尔会发生，从而产生基因顺序的变异。由于这37个基因所产生的可能的基因片段数目众多，因此，同一基因序列的趋同进化是罕见的，这表明mt基因片段是重建系统发育的良好分子标记。我确定了各种后生动物的线粒体基因组结构，主要是软体动物，并检查了基因顺序数据的系统发育效用。我的研究集中在腹足类，表现出高水平的变异性的线粒体基因组结构。我确定了完整的线粒体基因组的一个prosobranchNordotis的，后鳃蛹strigosa，两个heterostrophans Cingulina cingulata和Valvata hokkaidoensis和部分序列的许多肺，后鳃，和caenogastropodan类群。本研究表明腹足类中发生了广泛的基因组重组。基于对多板目Katharina tunicata和节肢动物Drosophila melanogaster的基因顺序数据的分支分析，我可以重建腹足类的系统发育。所构建的系统发育树与最近的解剖学数据一致，表明线粒体基因序列数据对系统发育重建是有用的。我还发现了几个基因顺序的变化发生在一个土地蜗牛超家庭螺旋。虽然基因顺序数据一直被认为是远缘类群的分子标记，但目前的数据表明，这类数据也可用于近缘类群的遗传学分析。

Metazoan mitochondrial DNA (mtDNA) is a closed circular molecule of approximately 16 kbp. This small genome normally encodes for 37 genes. Although mt-gene arrangements are usually conserved, genomic rearrangements occasionally occur to produce variation in the gene orders. Because of the inourmous numbers of possible gene arrangments produced by the 37 genes, convergent evolution of the same gene order must be rare, suggesting that mt-gene arrangments would be good molecular marker for phylogenetic reconstruction. I determined mt-genome structure for various metazoans, mainly mollscs, and examined phylogenetic utility of gene order data.My study focuses on gastropod which exhibit high level of variability in the mt-genome structure. I determined complete mt-genome for a prosobranch Nordotis gigantea, a opisthobranch Pupa strigosa, two heterostrophans Cingulina cingulata and Valvata hokkaidoensis and partial sequence of many pulmonate, opisthobanch, and caenogastropodan taxa. The present study demonstrated extensive genomic rearrangments to be occurred within gastropods. Based on cladistic analysis of gene order data using the polyplacophora Katharina tunicata and the arthropoda Drosophila melanogaster as outgroups, I could reconstruct gastropodan phylogeny. The proposed phylogentic tree was consistent with recent anatocimal data, indicating that mt-gene order data is useful for phylogenetic reconstruction. I also found several changes in the gene order to be occurred within a land snail superfamily Helicoidea. Althgough gene order data has been regarded as molecular marker for distantly related taxa, present data shows that such kind of data is also useful for phylogenetica analysis of much closer taxa.