中文摘要：

在鸟类线粒体基因组中，不同物种的线粒体碱基组成和特性存在明显的差异。截至2008年5月，Gen-Bank细胞器基因组资源数据库共公布了74种鸟类线粒体全基因组数据。本研究利用已公布的鸟类线粒体基因组全序列分析其碱基组成特征。结果表明：（1）鸟类线粒体基因组密码子第2位的GC含量值波动范围十分狭窄，而密码子第3位的GC含量值波动范围很大。（2）密码子第3位碱基中C的含量波动范围较大，为32．60％～50．70％。（3）线粒体基因组GC含量主要由密码子第3位的碱基C和T的变化引起。（4）密码子第3位碱基的GC含量与线粒体基因组的GC含量的变化存在相关性。本次结果为今后深入研究鸟类线粒体基因组提供了一定的借鉴和参考资料。

英文摘要：

The unusual feature of several species and heterogeneity of gene nucleotide content are common phenomena that exist in the avian mitochondrial genomes. In the present study, the base compositions of functional site over 74 avian mitochondrial genomes retrieved from GenBank Organelle Genome Resources on May 2008 were analyzed. The results showed as follow： （1） The GC-content at the third codon position typically showed the largest range of variation, while the GC-content at the second codon position was not subject to large fluctuation. （2） By ordering the species by increasing percentage of C, a very large variation in composition from 32.60% to 50.70% was observed. （3） Most major changes of GC-content in the whole genomes between species could be attributed to shifts between the proportions of C and T in the third position. （4） In addition, for each of the 74 species considered in this study, GC-content at the third codon position has been significant positive correlated with GC-content of the whole genome sequence. All of the results will provide fundamental information for further study on avian mitochondrial genome.