複製事件廣泛存在基因體的歷史當中，主導了基因序列的成長與演化。為了比較不同基因體間複製演化的共同特性，我們定義了序列的等價長度 l_e，等度價長度的直接意義即是，這個序列與長度 l_e 的隨機序列具有"等價的隨機性質"。也就是說，隨機序列的等價長度即等於自身的序列長，等價長度會在序列遭受隨機突變時增長，而在序列被複製時保持不變。 根據我們的研究，基因體具有普世的等價長度，且在染色體不同部分的等價長度皆相同，顯示原始的基因序列可能開始於一短序列，經由隨機片段複製作為演化動力而成長。這個結論與 RNA 世界假說相符合，而且能夠解釋存在先今基因體當中頻密的複製事件，或許也可為演化速率不平均的爭議提供解答。 Segmental duplication is widely held to be a dominant feature in the dynamics of genome growth and evolution. Yet how this would a ect the global structure of genomes has not been discused. Here, we identify the equivalent length, Le, of a genomic sequence as a medium through which that dominance may be discussed quantitatively. Through examining 865 complete chromosomes we nd the Le for a genomic sequence to be nearly invariant and remarkably short compared true sequence length { in terms of the statistics of two-letter words it is about 300 bases long { and is approximately universal for all (examined) complete chromosomes. We verify this result to be non-trivial, in particular, not caused by the similarity of sequences in any commonly held sense, and demonstrate that it is easy to generate genome-like sequences not having universal Le's. We establish a causal relation between short Le and segmental duplication and show that a simple, random-segmental-duplication driven model for genome growth generates highly diverse genome-like sequences that have universal Le's. We postulate a connection between the universal value of Le and maximum information capacity in genomic sequences and infer that the universality of Le is a crucial product of the evolution of genome toward maximum tness.
