The Red Queen theory of recombination hotspots.

Recombination hotspots are small chromosomal regions, where meiotic crossover events happen with high frequency. Recombination is initiated by a double-strand break (DSB) that requires the intervention of the molecular repair mechanism. The DSB repair mechanism may result in the exchange of homologous chromosomes (crossover) and the conversion of the allelic sequence that breaks into the one that does not break (biased gene conversion). Biased gene conversion results in a transmission advantage for the allele that does not break, thus preventing recombination and rendering recombination hotspots transient. How is it possible that recombination hotspots persist over evolutionary time (maintaining the average chromosomal crossover rate) when they are self-destructive? This fundamental question is known as the recombination hotspot paradox and has attracted much attention in recent years. Yet, that attention has not translated into a fully satisfactory answer. No existing model adequately explains all aspects of the recombination hotspot paradox. Here, we formulate an intragenomic conflict model resulting in Red Queen dynamics that fully accounts for all empirical observations regarding the molecular mechanisms of recombination hotspots, the nonrandom targeting of the recombination machinery to hotspots and the evolutionary dynamics of hotspot turnover.