The origin of meiotic sex was a key milestone in the evolution of the eukaryotic cell. The paralogous DNA recombinases Rad51 and meiosis-specific DMC1 are nearly universal among eukaryotes and have been used previously to trace the timing and origins of the meiotic machinery. Here we perform comparative genomics and phylogenetic analyses of Rad51 and DMC1 drawn from diverse eukaryotes with RadA recombinase sequences from a broad sampling of archaeal taxa, focusing on the recently sequenced diversity of Asgard archaeal taxa. We show that even with increased and new sampling, the eukaryotic Rad51 and DMC1 proteins still resolve separately from any archaeal RadA sequences. These findings suggest that the duplication of RadA into general and meiosis-specific paralogues occurred after the divergence of the eukaryotic progenitor and did not evolve at an earlier stage. These findings raise the important question of how the evolution of meiotic sex was linked to genome size expansion and the acquisition of the mitochondrial endosymbiont in early eukaryotes.

Centre for Life's Origins and Evolution Department of Genetics Evolution and Environment University College London London WC1E 6BT UK

Division of Infectious Diseases Department of Medicine and Department of Biological Sciences University of Alberta 1 124 Clinical Sciences Building 11350 83 Avenue Edmonton T6G 2G3 Canada

Institute of Parasitology Biology Centre Czech Academy of Sciences Ceské Budějovice 370 05 Czech Republic

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