Fine-scale crossover rate heterogeneity in Drosophila pseudoobscura.

Broad-scale differences in crossover rate across the genome have been characterized in most genomes studied. Fine-scale differences, however, have only been examined in a few taxa, such as Arabidopsis, yeast, humans, and mice. No prior studies have directly looked for fine-scale recombination rate heterogeneity in Drosophila. We produced 370 Drosophila pseudoobscura containing a crossover event within the 2-megabase (MB) region between the genes yellow and white. We then examined 19 intervals within this region and determined where the crossovers occurred. We found that recombination events occur nonrandomly on a small scale and that mild "hotspots" of a few kilobases exist in Drosophila. Among the regions studied, recombination rates varied from 1.4 to 52 cM/MB. We also observed a trend toward high codon bias in regions of high recombination. Finally, we identified a significantly positive correlation between recombination rate and simple repeats, as well as the motif CACAC. These sequence features may contribute to broad-scale variation in crossover rate and, thus, shed light on features associated with crossover rate heterogeneity at a genome-wide scale.