Repeat sequences limited lateral gene transfer and favored meiotic sex in early eukaryotes

The origin of meiotic sex is a long-standing evolutionary enigma. This novel mechanism of reproduction replaced lateral gene transfer (LGT), the uptake and recombination of pieces of environmental DNA seen in bacteria and archaea. We link its origin to the expanded genome size and proliferation of genetic repeats found in early eukaryotes. Both factors led to high levels of mutation accumulation and gene loss under LGT, which could not be retarded through increases in the rate of LGT or the length of DNA recombined. Meiotic sex with homologous pairing of long-chromosome-sized pieces of DNA promoted purifying selection and suppressed ectopic recombination. It permitted the evolution of the expanded genome needed for the evolution of complex eukaryotic life.

https://doi.org/10.1073/pnas.2205041119