RT Journal Article SR Electronic T1 Fine-scale crossover rate variation on the C. elegans X chromosome JF bioRxiv FD Cold Spring Harbor Laboratory SP 037317 DO 10.1101/037317 A1 Max R. Bernstein A1 Matthew V. Rockman YR 2016 UL http://biorxiv.org/content/early/2016/01/19/037317.abstract AB Meiotic recombination creates genotypic diversity within species. Recombination rates vary substantially across taxa and the distribution of crossovers can differ significantly among populations and between sexes. Crossover locations within species have been found to vary by chromosome and by position within chromosomes, where most crossover events occur in small regions known as recombination hotspots. However, several species appear to lack hotspots despite significant crossover heterogeneity. The nematode Caenorhabditis elegans was previously found to have the least fine-scale variation in crossover distribution among organisms studied to date. It is unclear whether this pattern extends to the X chromosome given its unique compaction through the pachytene stage of meiotic prophase in hermaphrodites. We generated 798 recombinant nested near-isogenic lines (NILs) with crossovers in a 1.41 Mb region on the left arm of the X chromosome to determine if its recombination landscape is similar to that of the autosomes. We find that the fine-scale variation in crossover rate is lower than that of other model species and is inconsistent with hotspots. The relationship of genomic features to crossover rate is dependent on scale, with GC content, histone modifications, and nucleosome occupancy being negatively associated with crossovers. We also find that the abundances of 4-6 base pair DNA motifs significantly explain crossover density. These results are consistent with recombination occurring at unevenly distributed sites of open chromatin.