中文摘要：

碱基组成是指基因组中腺嘌呤、鸟嘌呤、胞嘧啶和胸腺嘧啶的相对含量,一般用鸟嘌呤和胞嘧啶的含量（GC含量）表示。前人的研究表明,不同类群的核基因组GC含量存在差异,然而,对于动物线粒体基因组碱基组成的研究却很少。为此,本文统计和分析了分属于20个门的609个动物线粒体基因组的碱基组成。结果表明,各门动物间线粒体基因组GC含量没有显著差异,不能反映各动物门间的进化关系。脊椎动物鱼纲、两栖纲、爬行纲、鸟纲和哺乳纲及其代表性目的线粒体基因组GC含量虽有一定差异,但并未发现明显的变化规律。

英文摘要：

Base composition refers to the relative content of adenine, guanine, cytosine, and thymine within a genome, which is commonly represented by GC contents. Many previous studies demonstrated that the base compositions of nuclear genome as well as its features were variable in different phyla. However, few studies were concerned on the GC contents in animal mitochondrial genome. Hence, base compositions of 609 mitochondrial genomes belonged to 20 phyla were analyzed in this paper. The results indicated that the GC contents of mitochondrial genomes in animal phyla had no significant differ- ence and could not reflect the evolutionary relationships among them. Certain differences on GC contents were observed in the vertebrates （Pisces, Amphibia, Reptile, Ayes and Mammalia） , but no significant rules were found.