Lawrence Berkeley National Laboratory

Meiotic recombination rates can vary widely across genomes, with hotspots ofintense activity interspersed among cold regions. In yeast, hotspots tend to occur inpromoter regions of genes, whereas in humans and mice hotspots are largely definedby binding sites of the PRDM9 protein. To investigate the detailed recombinationpattern in a flowering plant we use shotgun resequencing of a wild population of themonkeyflower Mimulus guttatus to precisely locate over 400,000 boundaries ofhistoric crossovers or gene conversion tracts. Their distribution defines some 13,000hotspots of varying strengths, interspersed with cold regions of undetectably lowrecombination. Average recombination rates peak near starts of genes and fall offsharply, exhibiting polarity. Within genes, recombination tracts are more likely toterminate in exons than in introns. The general pattern is similar to that observed inyeast, as well as in PRDM9-knockout mice, suggesting that recombination initiationdescribed here in Mimulus may reflect ancient and conserved eukaryoticmechanisms