Lynch Michael, Conery John S
Dept. of Biology, Indiana University, Bloomington, Indiana 47405, USA.
J Struct Funct Genomics. 2003;3(1-4):35-44.
Although gene duplication has generally been viewed as a necessary source of material for the origin of evolutionary novelties, the rates of origin, loss, and preservation of gene duplicates are not well understood. Applying steady-state demographic techniques to the age distributions of duplicate genes censused in seven completely sequenced genomes, we estimate the average rate of duplication of a eukaryotic gene to be on the order of 0.01/ gene/million years, which is of the same order of magnitude as the mutation rate per nucleotide site. However, the average half-life of duplicate genes is relatively small, on the order of 4.0 million years. Significant interspecific variation in these rates appears to be responsible for differences in species-specific genome sizes that arise as a consequence of a quasi-equilibrium birth-death process. Most duplicated genes experience a brief period of relaxed selection early in their history and a minority exhibit the signature of directional selection, but those that survive more than a few million years eventually experience strong purifying selection. Thus, although most theoretical work on the gene-duplication process has focused on issues related to adaptive evolution, the origin of a new function appears to be a very rare fate for a duplicate gene. A more significant role of the duplication process may be the generation of microchromosomal rearrangements through reciprocal silencing of alternative copies, which can lead to the passive origin of post-zygotic reproductive barriers in descendant lineages of incipient species.
尽管基因复制通常被视为进化新特征起源的必要物质来源，但基因复制产物的起源、丢失和保留速率尚未得到很好的理解。我们将稳态人口统计学技术应用于对七个完全测序基因组中普查的复制基因的年龄分布分析，估计真核基因的平均复制速率约为每基因每百万年0.01次，这与每核苷酸位点的突变率处于同一数量级。然而，复制基因的平均半衰期相对较短，约为400万年。这些速率的显著种间差异似乎是由于准平衡的出生-死亡过程导致的物种特异性基因组大小差异的原因。大多数复制基因在其历史早期经历一段短暂的选择放松期，少数基因表现出定向选择的特征，但那些存活超过几百万年的基因最终会经历强烈的纯化选择。因此，尽管关于基因复制过程的大多数理论工作都集中在与适应性进化相关的问题上，但新功能的起源似乎是复制基因非常罕见的命运。复制过程更重要的作用可能是通过对替代拷贝的相互沉默产生微染色体重排，这可能导致初始物种后代谱系中合子后生殖隔离的被动起源。
