rec-1 loss of function is insufficient to homogenize crossover distribution in Caenorhabditis elegans

Meiotic control of crossover (CO) position is critical for proper homologous chromosome segregation and organismal fertility, recombination of parental genotypes, and the generation of novel genetic combinations. We here characterize the recombination rate landscape of a loss of function genetic modifier of CO position in Caernorhabditis elegans. By averaging CO position across hermaphrodite and male meioses and by genotyping 203 single-nucleotide variants covering about 95% of the genome, we find that the characteristic chromosomal arm-center recombination rate domain structure is lost in a loss of function rec-1 mutant. The rec-1 loss of function mutant smooths the recombination rate landscape but is insufficient to eliminate the non-uniform position of CO. We further find that the rec-1 mutant is of little consequence for organismal fertility and embryo hatchability and thus for rates of autosomal non-disjunction. However, it specifically increases X chromosome non-disjunction rates and males appearance. Our findings question the maintenance of genetic diversity among C. elegans natural populations, and they further suggest that manipulating genetic modifiers of CO position will help map quantitative trait loci in low-recombining genomic regions.