Evolution of Sexual Reproduction: Importance of DNA Repair, Complementation, and Variation

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Abstract
Sexual reproduction probably arose in evolution as a DNA repair process which allowed damage in 1 chromosome to be repaired by the information in another homologous chromosome, and has retained this advantage throughout evolution. Since this process required that 2 chromosomes be present in a common cytoplasm, additional ways evolved to take advantage of the redundant information available. The diploid stage of the cycle probably was transient in early organisms, but began to take on a more significant role as genome size increased, since it provided protection against the expression of deleterious mutations. As the diploid stage of the sexual cycle became the predominant stage, genome information content expanded beyond the range of haploid organisms. The shift to diploidy is essentially irreversible, and helps prevent the abandonment of sexual reproduction. A consequence of the DNA exchange reactions that constitute recombinational repair is the reassortment of parental genetic information among progeny. This variation is advantageous under certain conditions. A complete evolutionary explanation for the maintenance of sexual reproduction also should include complementation and DNA repair.