The evolutionary mechanism of genome size
The evolutionary mechanism of genome size
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DOI：
10.1360/n972016-00728
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发表时间：
2016-08
影响因子：
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通讯作者：
Mijuan Shi;Yingyin Cheng;Wanting Zhang;Xiaoqin Xia
中科院分区：
文献类型：
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作者：
Mijuan Shi;Yingyin Cheng;Wanting Zhang;Xiaoqin Xia
基因组是一组编码生物体完整遗传信息的DNA序列，因此更复杂的生物体有理由拥有更大的基因组。然而，真核生物基因组大小变化巨大，似乎与进化复杂性无关。它们之间的这种不一致被称为c值悖论。本文简要介绍了基因组大小的研究历史，并对基因组大小与进化水平、基因组组成及细胞性状关系的研究进展和假设进行了综述。在生物分类的最高层次上，进化复杂性的增加明显伴随着遗传信息的增加，从而导致更大的基因组大小。尽管邻近群体之间存在重叠，但随着进化复杂性的增加，基因组大小的排序也随之上升，即病毒的顺式调控元件位点、更多可选择的剪接基因型和更高的等位基因交换频率，因此赋予了群体更高的遗传多样性和环境适应性。因此，非编码DNA序列可以在进化过程中积累在基因组上，因为它们可以促进基因的优化和生物体的进化。非编码DNA的大量插入并没有明显地改变生物体的进化复杂性，但却打断了基因组大小与进化复杂性之间的相关性，从而导致了所谓的c值悖论。基因组大小的进化机制通常由两种主要假设来解释：自然选择理论和遗传漂变的中性理论。我们认为，前者在中尺度上决定了基因组大小的显著变化，后者在微观尺度上决定了基因组大小的波动。分子事件可能以多种方式影响基因组大小。虽然突变率和作为转座子的重复序列旨在扩大基因组，但某些机制，例如piRNA可以阻止基因组的生长。我们强调分子变异带来基因组大小的变化，有利的变化被自然选择保留。
A genome is a set of DNA sequences encoding the complete genetic information of an organism, therefore more complex organisms are reasonably expected to have larger genomes. However, eukaryotic genome size vary drastically and seems to have no connection to the evolutionary complexity. Such an inconsistency between them is known as the C-value paradox. Here we briefly introduced the history of researches on genome size, and reviewed the advances and hypotheses of the researches on the relationships between genome size and evolutionary level, genome composition and some cell traits. At the top level of biological classification, the increase of evolutionary complexity is notably coupled with the augment of genetic information which leads to bigger genome sizes. Albeit there are overlapping between adjacent groups, the genome sizes rank upwards as evolutionary complexity, i.e, viruses cis -regulatory element sites, more alternative splicing genotypes, and higher allele exchange frequency, therefore endows a population higher genetic diversity and environmental adaptability. Thus noncoding DNA sequences can be accumulated on genome during evolution because they may promote the optimization of genes and the evolution of an organism. The bulk insertion of noncoding DNA does not apparently change an organism’s evolution complexity, but interrupts the correlation between genome size and evolutionary complexity, thereafter leads to the so-called C-value paradox. The evolutionary mechanism of genome size is often explained by two primary hypotheses: the natural selection theory and the neutral theory with genetic drift. We believe the former determines the significant changes in genome size on a mesoscale and the latter contributes to fluctuations in the genome size on a microscale. Molecular events may impose on genome size in diversified ways. While mutation rate and repeated sequences as transposons intend to enlarge genomes, some mechanism, as an example, piRNA can prevent a genome from growing. We emphasize the point that molecular variations bring changes to the genome size and advantageous changes be retained by natural selection.