The Department of Genetics, The Alexander Silberman Institute of Life Sciences, The Hebrew University of Jerusalem, Edmond J. Safra Campus, Jerusalem, 9190401, Israel.
Biol Rev Camb Philos Soc. 2018 May;93(2):801-810. doi: 10.1111/brv.12367. Epub 2017 Sep 14.
Ever since Darwin first addressed it, sexual reproduction reigns as the 'queen' of evolutionary questions. Multiple theories tried to explain how this apparently costly and cumbersome method has become the universal mode of eukaryote reproduction. Most theories stress the adaptive advantages of sex by generating variation, they fail however to explain the ubiquitous persistence of sexual reproduction also where adaptation is not an issue. I argue that the obstacle for comprehending the role of sex stems from the conceptual entanglement of two distinct processes - gamete production by meiosis and gamete fusion by mating (mixis). Meiosis is an ancient, highly rigid and evolutionary conserved process identical and ubiquitous in all eukaryotes. Mating, by contrast, shows tremendous evolutionary variability even in closely related clades and exhibits wonderful ecological adaptability. To appreciate the respective roles of these two processes, which are normally linked and alternating, we require cases where one takes place without the other. Such cases are rather common. The heteromorphic sex chromosomes Y and W, that do not undergo meiotic recombination are an evolutionary test case for demonstrating the role of meiosis. Substantial recent genomic evidence highlights the accelerated rates of change and attrition these chromosomes undergo in comparison to those of recombining autosomes. I thus propose that the most basic role of meiosis is conserving integrity of the genome. A reciprocal case of meiosis without bi-parental mating, is presented by self-fertilization, which is fairly common in flowering plants, as well as most types of apomixis. I argue that deconstructing sex into these two distinct processes - meiosis and mating - will greatly facilitate their analysis and promote our understanding of sexual reproduction.
自从达尔文首次提出这个问题以来，有性生殖一直是进化问题的“女王”。有许多理论试图解释这种明显代价高昂且繁琐的方法是如何成为真核生物生殖的普遍模式的。大多数理论强调了性的适应性优势，通过产生变异来解释，然而，它们无法解释在适应不是问题的情况下，有性生殖普遍存在的原因。我认为，理解性的作用的障碍源于两个不同过程的概念上的纠缠——减数分裂产生配子和交配（融合）产生配子。减数分裂是一个古老的、高度刚性的和进化上保守的过程，在所有真核生物中都是相同且普遍存在的。相比之下，交配表现出巨大的进化变异性，即使在密切相关的进化枝中也是如此，并且表现出出色的生态适应性。为了理解这两个通常是相互联系和交替的过程各自的作用，我们需要一些一个过程发生而另一个过程不发生的情况。这种情况相当普遍。性染色体 Y 和 W 是异态的，不经历减数分裂重组，是展示减数分裂作用的进化测试案例。最近大量的基因组证据强调了这些染色体与重组的常染色体相比经历的快速变化和损耗率。因此，我提出减数分裂的最基本作用是保持基因组的完整性。减数分裂而没有双亲交配的反例是自交，它在开花植物中相当普遍，以及大多数类型的无融合生殖中也是如此。我认为，将性分解为这两个不同的过程——减数分裂和交配，将极大地促进对它们的分析，并促进我们对有性生殖的理解。
