中文摘要：

在脱氧核糖核酸（DNA）一级序列中，4种碱基可以有16种两两组合的方式（例如，ct，ag，cg，tc等），不同的组合方式在DNA的该种序列中出现的次数也不一样，其中，cg出现的频数甚少．本文将cg所处位置及频率作为一种数学的量，计算了各物种的分子连接件指数，并以之为参数进行了物种间相似件分析．在此基础上进一步对10种物种做了分组和归类．

英文摘要：

There are 16 ways for 4 kinds of bases to combine as a pair within DNA primary sequence （for example, ct, ag, cg, tc and so on.）, and the frequencies of occurrences of different pairs in sequence are not the same. Especially, the frequency of cg is very low. In this article, we take the frequency of cg as parameter and calculate the molecular connectivity indices. Then, we compare the sequences of 10 species based on the indices and group them into different classes. The results agree with the phylogenetic tree satisfactorily.