Hughes Austin L, Friedman Robert
Department of Biological Sciences, University of South Carolina, Columbia, SC 29208, USA.
J Struct Funct Genomics. 2003;3(1-4):85-93.
The widely popular hypothesis that there were two rounds of genome duplication by polyploidization early in vertebrate history (the 2R hypothesis) has been difficult to test until recently. Among the lines of evidence adduced in support of this hypothesis are relative genome size, relative gene number, and the existence of genomic regions putatively duplicated during polyploidization. The availability of sequence for a substantial portion of the human genome makes possible the first rigorous tests of this hypothesis. Comparison of gene family size in the human genome and in invertebrate genomes shows no evidence of a 4:1 ratio between vertebrates and invertebrates. Furthermore, explicit phylogenetic tests for the topology expected from two rounds of polyploidization have revealed alternative topologies in a substantial majority of human gene families. Likewise, phylogenetic analyses have shown that putatively duplicated genomic regions often include genes duplicated at widely different times over the evolution of life. The 2R hypothesis thus can be decisively rejected. Rather, current evidence favors a model of genome evolution in which tandem duplication, whether of genomic segments or of individual genes, predominates.
脊椎动物早期历史中通过多倍体化进行两轮基因组复制的假说（2R假说）广受欢迎，但直到最近都难以验证。支持这一假说的证据包括相对基因组大小、相对基因数量以及多倍体化期间假定复制的基因组区域的存在。人类基因组很大一部分序列的可得性使得首次对这一假说进行严格验证成为可能。对人类基因组和无脊椎动物基因组中基因家族大小的比较表明，没有证据显示脊椎动物和无脊椎动物之间存在4:1的比例。此外，针对两轮多倍体化预期拓扑结构的明确系统发育测试在绝大多数人类基因家族中揭示了其他拓扑结构。同样，系统发育分析表明假定复制的基因组区域通常包含在生命进化过程中不同时间复制的基因。因此，2R假说可以被明确拒绝。相反，目前的证据支持一种基因组进化模型，即串联复制，无论是基因组片段还是单个基因的串联复制，占主导地位。
