Korunes Katharine L, Noor Mohamed A F
Department of Biology, Duke University, Box 90338, Durham, NC, 27708, USA.
Mol Ecol. 2017 Jan;26(1):351-364. doi: 10.1111/mec.13736. Epub 2016 Jul 29.
Crossing over is well known to have profound effects on patterns of genetic diversity and genome evolution. Far less direct attention has been paid to another distinct outcome of meiotic recombination: noncrossover gene conversion (NCGC). Crossing over and NCGC both shuffle combinations of alleles, and this degradation of linkage disequilibrium (LD) has major evolutionary consequences, ranging from immediate effects on nucleotide diversity to long-term consequences that shape genome evolution, species formation and species persistence. Unlike simple crossing over, NCGC has the potential to alter allele frequencies. Gene conversion can also occur in genomic regions where crossing over does not, and it purportedly exhibits more uniform rates across genomes. Considerable progress has been made towards understanding the mechanisms of gene conversion, and this progress enables us to begin exploring how gene conversion affects processes such as molecular evolution and interspecies gene flow. These topics are timely with the recent shift in focus from a primarily neutral null model of molecular evolution and speciation to one incorporating base levels of selection, making it all the more crucial to understand the basis and evolutionary implications of linkage. Here, we discuss the impact of gene conversion on genome structure and evolution and the current methods for detecting these events. We provide a comprehensive review of how gene conversion breaks down LD and affects both short- and long-term evolutionary processes, and we contrast its impact to that expected from crossing over alone.
众所周知，交叉互换对遗传多样性模式和基因组进化有着深远影响。而减数分裂重组的另一个独特结果——非交叉基因转换（NCGC），受到的直接关注则少得多。交叉互换和NCGC都会打乱等位基因的组合，这种连锁不平衡（LD）的破坏具有重大的进化后果，从对核苷酸多样性的直接影响到塑造基因组进化、物种形成和物种存续的长期后果。与简单的交叉互换不同，NCGC有可能改变等位基因频率。基因转换也可发生在不发生交叉互换的基因组区域，而且据称其在基因组中的发生率更为均匀。在理解基因转换机制方面已经取得了相当大的进展，这使我们能够开始探索基因转换如何影响分子进化和种间基因流动等过程。随着近期研究重点从主要基于中性的分子进化和物种形成零模型转向纳入基本选择水平的模型，这些话题正逢其时，因此理解连锁的基础及其进化意义变得更加关键。在这里，我们讨论基因转换对基因组结构和进化的影响以及检测这些事件的当前方法。我们全面综述了基因转换如何打破LD并影响短期和长期进化过程，并将其影响与仅由交叉互换所预期的影响进行对比。
