Factors influencing recombination frequency and distribution in a human meiotic crossover hotspot

Little is known about the factors that influence the frequency and distribution of meiotic recombination events within human crossover hotspots. We now describe the detailed analysis of sperm recombination in the NID1 hotspot. Like the neighbouring MS32 hotspot, the NID1 hotspot is associated with a minisatellite, suggesting that hotspots predispose DNA to tandem repetition. Unlike MS32, crossover resolution break-points in NID1 avoid the minisatellite, producing a cold spot within the hotspot. This avoidance may be related to the palindromic nature of the minisatellite interfering with the generation and/or processing of recombination intermediates. The NID1 hotspot also contains a single nucleotide polymorphism (SNP) close to the centre, which appears to directly influence the frequency of crossover initiation. Quantitative gene conversion assays show that this SNP affects the frequency of gene conversion and crossover to a very similar extent, providing evidence that conversions and crossovers are triggered by the same recombi-nation initiating events. The recombination-suppressing allele is over-transmitted to recombinant progeny, and provides the most dramatic example to date of recombination-mediated meiotic drive, of a magnitude sufficient to virtually guarantee that the recombination suppressor will eventually replace the more active allele in human populations