From the initial application of molecular techniques to the study of microbial organisms, three domains of life emerged, with eukaryotes and archaea as sister taxa. However, recent analyses of an expanding molecular data set reveal that the eukaryotic genome is chimeric with respect to archaea and bacteria. Moreover, there is now evidence that the primitive eukaryotic group `Archezoa' once harbored mitochondia. These discoveries have challenged the traditional stepwise model of the evolution of eukaryotes, in which the nucleus and microtubules evolve before the acquisition of mitochondria, and consequently compel a revision of existing models of the origin of eukaryotic cells.

中文翻译：

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对真核生物起源的看法不断变化。

从最初的分子技术应用到微生物研究，出现了三个生命领域，其中真核生物和古细菌为姐妹类群。但是，最近对扩展的分子数据集的分析表明，真核生物基因组在古细菌和细菌方面是嵌合的。而且，现在有证据表明原始的真核生物群“ Archezoa”曾经藏有线粒体。这些发现挑战了真核生物进化的传统逐步模型，在这种模型中，核和微管在线粒体获得之前就已经进化，因此迫使对真核细胞起源的现有模型进行修订。