Department of Systematic and Evolutionary Botany, University of Vienna, Austria.
Heredity (Edinb). 2009 Dec;103(6):445-57. doi: 10.1038/hdy.2009.85. Epub 2009 Jul 22.
Sexual reproduction implies high costs, but it is difficult to give evidence for evolutionary advantages that would explain the predominance of meiotic sex in eukaryotes. A combinational theory discussing evolution, maintenance and loss of sex may resolve the problem. The main function of sex is the restoration of DNA and consequently a higher quality of offspring. Recombination at meiosis evolved, perhaps, as a repair mechanism of DNA strand damages. This mechanism is most efficient for DNA restoration in multicellular eukaryotes, because the initial cell starts with a re-optimized genome, which is passed to all the daughter cells. Meiosis acts also as creator of variation in haploid stages, in which selection can purge most efficiently deleterious mutations. A prolonged diploid phase buffers the effects of deleterious recessive alleles as well as epigenetic defects and is thus optimal for prolonged growth periods. For complex multicellular organisms, the main advantage of sexuality is thus the alternation of diploid and haploid stages, combining advantages of both. A loss of sex is constrained by several, partly group-specific, developmental features. Hybridization may trigger shifts from sexual to asexual reproduction, but crossing barriers of the parental sexual species limit this process. For the concerted break-up of meiosis-outcrossing cycles plus silencing of secondary features, various group-specific changes in the regulatory system may be required. An establishment of asexuals requires special functional modifications and environmental opportunities. Costs for maintenance of meiotic sex are consequently lower than a shift to asexual reproduction.
有性生殖意味着高成本，但很难找到进化优势的证据来解释减数分裂有性生殖在真核生物中的主导地位。一个综合的讨论进化、维持和丧失有性生殖的理论可能会解决这个问题。有性生殖的主要功能是修复 DNA，从而产生更高质量的后代。减数分裂的重组可能是作为 DNA 链损伤的修复机制而进化的。这种机制在多细胞真核生物中对于 DNA 修复最为有效，因为起始细胞从一个重新优化的基因组开始，这个基因组被传递给所有的子细胞。减数分裂在单倍体阶段也充当了变异的创造者，在这个阶段选择可以最有效地清除有害突变。延长的二倍体阶段缓冲了有害隐性等位基因以及表观遗传缺陷的影响，因此对于延长的生长周期是最佳的。对于复杂的多细胞生物来说，有性生殖的主要优势是二倍体和单倍体阶段的交替，结合了两者的优势。丧失有性生殖受到几个部分群体特异性、发育特征的限制。杂交可能会引发从有性生殖到无性生殖的转变，但亲本性生殖物种的杂交障碍限制了这个过程。为了协调减数分裂异交周期的中断和次要特征的沉默，调节系统可能需要发生各种群体特异性的变化。无性生殖的建立需要特殊的功能修改和环境机会。因此，维持减数分裂有性生殖的成本比转向无性生殖要低。
