Szathmáry E, Kövér S
Department of Plant Taxonomy and Ecology, Eötvös University, Budapest, Hungary.
Genet Res. 1991 Oct;58(2):157-65. doi: 10.1017/s0016672300029815.
The DNA repair hypothesis for the maintenance of sex states that recombination is necessary for the repair of double-strand DNA damage. In a closed (mitotic) genetic system crossing-over generates homozygosity. This reduces fitness if deleterious recessive alleles become expressed. Thus, outcrossing is required to restore heterozygosity destroyed by recombination. The repair hypothesis is tested by comparing outcrossing sexuality with a hypothetical parthenogenic strategy (the Prudent Reparator) which destroys as little heterozygosity during repair as possible. In the Prudent Reparator, repair of double-strand DNA damage results in a small amount of homozygosity due to gene conversion only, since this process does not render outside markers homozygous. Diploidy, deleterious recessives, multiplicative fitness and linkage equilibrium in mutation-selection balance are assumed. The average fitness of this population increases, and complementation (i.e. masking of recessives in heterozygous form) decreases with the rate of damage per locus. The equilibrium fitness of the Prudent Reparator can be well above that of the sexual population. A lower complementation ability of parthenogens may not be an impenetrable barrier to their successful establishment if the invader's genome is relatively uncontaminated by mutant alleles: there are always such genotypes in the sexual population. Thus, the Prudent Reparator could solve the problem of repairing damage as well as that of invading an existing outcrossing population. As we do not see this strategy widely adopted instead of sexuality, the repair hypothesis is likely to miss some essential feature of the evolution of sex.
维持性别的DNA修复假说认为，重组对于双链DNA损伤的修复是必要的。在一个封闭的（有丝分裂）遗传系统中，交叉会产生纯合性。如果有害的隐性等位基因得以表达，这会降低适应性。因此，需要异交来恢复因重组而被破坏的杂合性。通过将异交性行为与一种假设的孤雌生殖策略（谨慎修复者）进行比较来检验修复假说，该策略在修复过程中尽可能少地破坏杂合性。在谨慎修复者中，双链DNA损伤的修复仅由于基因转换而导致少量纯合性，因为这个过程不会使外部标记变为纯合。假设存在二倍体、有害隐性基因、乘法适应性以及突变 - 选择平衡中的连锁平衡。这个种群的平均适应性会增加，并且互补作用（即杂合形式中隐性基因的掩盖）会随着每个位点的损伤率而降低。谨慎修复者的平衡适应性可能远高于有性种群。如果入侵者的基因组相对未被突变等位基因污染，孤雌生殖者较低的互补能力可能并不是其成功建立的不可逾越的障碍：有性种群中总是存在这样的基因型。因此，谨慎修复者既能解决修复损伤的问题，也能解决入侵现有的异交种群的问题。由于我们没有看到这种策略被广泛采用来取代有性生殖，所以修复假说可能遗漏了性别进化的一些基本特征。
