Data from: Meta‐analysis of chromosome‐scale crossover rate variation in eukaryotes and its significance to evolutionary genomics

Understanding the distribution of crossovers along chromosomes is crucial to evolutionary genomics because the crossover rate determines how strongly a genome region is influenced by natural selection. Nevertheless, generalities in the chromosome-scale distribution of crossovers have not been investigated formally. We fill this gap by synthesizing joint information on genetic and physical maps across 62 animal, plant, and fungal species. Our quantitative analysis reveals a strong and taxonomically wide-spread reduction of the crossover rate in the center of chromosomes relative to their peripheries. We demonstrate that this pattern is poorly explained by the position of the centromere, but find that the magnitude of the relative reduction in the crossover rate in chromosome centers increases with chromosome length. That is, long chromosomes often display a dramatically low crossover rate in their center whereas short chromosomes exhibit a relatively homogeneous crossover rate. This observation is compatible with a model in which crossovers are initiated from the chromosome tips, an idea with preliminary support from mechanistic investigations of meiotic recombination. Consequently, we show that organisms achieve a higher genome-wide crossover rate by evolving smaller chromosomes. Summarizing theory and providing empirical examples, we finally highlight that taxonomically wide-spread and systematic heterogeneity in crossover rate along chromosomes generates predictable broad-scale trends in genetic diversity and population differentiation by modifying the impact of natural selection among regions within a genome. We conclude by emphasizing that chromosome-scale heterogeneity in crossover rate should urgently be incorporated into analytical tools in evolutionary genomics, and in the interpretation of emerging patterns.解析染色体上染色体交换（crossover）事件的分布规律对进化基因组学至关重要，因为交换率决定了基因组区域受自然选择作用的强度。然而，学界尚未正式探究染色体尺度下交换分布的通用模式。本研究整合了62个动物、植物与真菌物种的遗传图谱与物理图谱的联合信息，填补了这一研究空白。我们的定量分析揭示了一个显著且跨分类群广泛存在的模式：相较于染色体的末端区域，染色体中心区域的交换率显著降低。进一步分析表明，着丝粒位置无法很好解释这一模式，但我们发现染色体中心区交换率的相对下降幅度随染色体长度增加而增大，即长染色体的中心区域往往交换率极低，而短染色体的交换率则相对均匀。这一观测结果与"交换事件由染色体末端起始"的模型相符，该假说已得到减数分裂重组机制研究的初步支持。据此我们发现，生物可通过演化出更小的染色体来提升全基因组的交换率。本研究在总结相关理论的同时提供了实证案例，最终强调：染色体尺度上交换率的系统性且广泛存在的异质性，会通过改变基因组不同区域受自然选择的影响程度，在遗传多样性与种群分化方面产生可预测的宏观趋势。我们在文末指出，亟须将染色体尺度的交换率异质性纳入进化基因组学的分析工具与新兴演化模式的解读框架中。