The Origin and the Adaptive Function of Genetic Recombination in Sexual Reproduction

Genetic recombination occurs in many organisms, from simple RNA viruses to mammals and plants with DNA genomes. In sexual reproduction, two parental genomes come together and undergo recombination, producing an offspring genome with a combination of information from the two parental genomes. Genome recombination that occurs during sexual reproduction can involve any one of several mechanisms, including copy-choice recombination as well as breakage and exchange. Across widely different organisms, recombination is generally promoted by factors that damage the genetic material. In organisms such as bacteriophage and Paramecium, it was experimentally demonstrated that recombinational repair during sexual reproduction can overcome otherwise deleterious or lethal damage. For many decades, it has been recognized that there are higher biological costs of sexual reproduction than for asexual reproduction. Theories assuming that genetic variation, due to recombination, is the main adaptive benefit of sexual reproduction have been widely accepted. Such a benefit was considered to compensate for the high cost of sexual reproduction. However, it has been difficult to find a strong, consistent benefit of variation. The repair of lethal damage, involving recombinational interactions of two different genomes, now appears to be the major selective factor underlying sexual reproduction in organisms both simple and complex.