Williams, Amy LGenovese, GiulioDyer, ThomasAltemose, NicolasTruax, KatherineJun, GooPatterson, NickMyers, Simon RCurran, Joanne EDuggirala, RaviBlangero, JohnReich, DavidPrzeworski, Molly2015-05-042015Williams, A. L., G. Genovese, T. Dyer, N. Altemose, K. Truax, G. Jun, N. Patterson, et al. 2015. “Non-crossover gene conversions show strong GC bias and unexpected clustering in humans.” eLife 4 (1): e04637. doi:10.7554/eLife.04637. http://dx.doi.org/10.7554/eLife.04637.2050-084Xhttp://nrs.harvard.edu/urn-3:HUL.InstRepos:15034775Although the past decade has seen tremendous progress in our understanding of fine-scale recombination, little is known about non-crossover (NCO) gene conversion. We report the first genome-wide study of NCO events in humans. Using SNP array data from 98 meioses, we identified 103 sites affected by NCO, of which 50/52 were confirmed in sequence data. Overlap with double strand break (DSB) hotspots indicates that most of the events are likely of meiotic origin. We estimate that a site is involved in a NCO at a rate of 5.9 × 10−6/bp/generation, consistent with sperm-typing studies, and infer that tract lengths span at least an order of magnitude. Observed NCO events show strong allelic bias at heterozygous AT/GC SNPs, with 68% (58–78%) transmitting GC alleles (p = 5 × 10−4). Strikingly, in 4 of 15 regions with resequencing data, multiple disjoint NCO tracts cluster in close proximity (∼20–30 kb), a phenomenon not previously seen in mammals. DOI: http://dx.doi.org/10.7554/eLife.04637.001en-USrecombinationnon-crossovergene conversionGC-biascomplex crossoverhaplotypeshumanJournal Article2015-05-0410.7554/eLife.04637