Meiosis decreases recombination load; Mitosis increases recombination load

Chiasmata are necessary for proper chromosomal segregation, but can result in inadvertent recombination. Bernstein and Michod demonstrated that meiosis evolved as a means of error correction, not genetic mixing. Therefore meiotic recombination is not the sine qua non of sex, but is instead an epiphenomenon of imperfect meiotic error correction. By correcting against recombinant genotypes, meiosis reduces recombination load, thereby providing an unappreciated selective advantage for sex. Sex reducing recombination load should be integrated into population genetic models of multi-locus epistasis for maintenance of sex and may explain sequestration of germ lines in animals. We predict that eumetazoa have less recombination load than sexual organisms without a germ line. Mitosis largely lacks the error correction of meiosis, destroys linkage through ubiquitous mitotic recombination, and thereby increases recombination load, especially in co-adapted gene complexes. Meiosis and possibly karyogamy provide an unexpected benefit to sex, offsetting at least some of the famed costs of sex.