Intermixing of genomes through meiotic reassortment and recombination of homologous chromosomes is a unifying theme of sexual reproduction in eukaryotic organisms and is considered crucial for their adaptive evolution. Previous studies of the budding yeast species Saccharomycodes ludwigii suggested that meiotic crossing over might be absent from its sexual life cycle, which is predominated by fertilization within the meiotic tetrad. We demonstrate that recombination is extremely suppressed during meiosis in Sd. ludwigii. DNA double-strand break formation by the conserved transesterase Spo11, processing and repair involving interhomolog interactions are required for normal meiosis but do not lead to crossing over. Although the species has retained an intact meiotic gene repertoire, genetic and population analyses suggest the exceptionally rare occurrence of meiotic crossovers in its genome. A strong AT bias of spontaneous mutations and the absence of recombination are likely responsible for its unusually low genomic GC level. Sd. ludwigii has followed a unique evolutionary trajectory that possibly derives fitness benefits from the combination of frequent mating between products of the same meiotic event with the extreme suppression of meiotic recombination. This life style ensures preservation of heterozygosity throughout its genome and may enable the species to adapt to its environment and survive with only minimal levels of rare meiotic recombination. We propose Sd. ludwigii as an excellent natural forum for the study of genome evolution and recombination rates.

中文翻译：

---

路德维希酵母中无交叉的性交


通过减数分裂重配和同源染色体重组实现基因组混合是真核生物有性生殖的统一主题，被认为对其适应性进化至关重要。先前对出芽酵母种路德维希酵母的研究表明，其有性生命周期中可能不存在减数分裂交叉，而减数分裂四分体内的受精占主导地位。我们证明 Sd 减数分裂期间重组受到极大抑制。路德维希。保守的酯交换酶 Spo11 形成 DNA 双链断裂，涉及同源间相互作用的加工和修复是正常减数分裂所必需的，但不会导致交换。尽管该物种保留了完整的减数分裂基因库，但遗传和种群分析表明其基因组中减数分裂交叉的发生异常罕见。自发突变的强烈 AT 偏向和重组的缺乏可能是其基因组 GC 水平异常低的原因。 Sd。路德维希遵循了独特的进化轨迹，该轨迹可能通过同一减数分裂事件的产物之间的频繁交配与减数分裂重组的极度抑制相结合而获得适应性益处。这种生活方式确保了整个基因组杂合性的保存，并且可能使物种能够适应其环境并仅以最低水平的罕见减数分裂重组生存。我们建议 Sd。 ludwigii 是研究基因组进化和重组率的绝佳天然论坛。