Non-crossover gene conversions show strong GC bias and unexpected clustering in humans

Amy Williams, Giulio Geneovese, Thomas Dyer, Katherine Truax, Goo Jun, Nick Patterson, Joanne E. Curran, Ravi Duggirala, John Blangero, David Reich, Molly Przeworski,
doi: http://dx.doi.org/10.1101/009175

Although the past decade has seen tremendous progress in our understanding of fine-scale recombination, little is known about non-crossover (or “gene conversion”) resolutions. We report the first genome-wide study of non-crossover gene conversion events in humans. Using SNP array data from 94 meioses, we identified 107 sites affected by non-crossover events, of which 51/53 were confirmed in sequence data. Our results suggest that a site is involved in a non-crossover event at a rate of 6.7 × 10-6/bp/generation, consistent with results from sperm-typing studies. Observed non-crossover events show strong allelic bias, with 70% (61–79%) of events transmitting GC alleles (P=7.9 × 10-5), and have tracts lengths that vary over more than an order of magnitude. Strikingly, in 4 of 15 regions with available resequencing data, multiple (~2–4) distinct non-crossover events cluster within ~20–30 kb. This pattern has not been reported previously in mammals and is inconsistent with canonical models of double strand break repair.