Origin and Adaptive Function of Genetic Recombination in Sexual Reproduction

Genetic recombination occurs in a wide range of 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 that has a combination of information from the two parental genomes. Genome recombination occurring during sexual reproduction can involve one of several mechanisms, including copy-choice recombination as well as breakage and exchange. Across widely different organisms, recombination by any mechanism 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 damages. For many decades it has been recognized that there are larger biological costs of sexual reproduction than for asexual reproduction. Much effort has been invested in theories assuming that genetic variation, due to recombination, is the main adaptive benefit of sexual reproduction. Such a benefit was considered to compensate for the large costs of sexual reproduction. However, it has been difficult to find a strong consistent benefit for variation. Repair of lethal damages, involving recombiantional interactions of two different genomes, now appears to be the major selective factor underlying sexual reproduction in organisms both simple and complex.