Recombinational Repair May Be an Important Function of Sexual Reproduction

Many different organisms are known to repair their DNA. implying that this ability is widespread in nature and suggesting that DNA damage is a general biological problem. In higher organisms selective pressures to minimize DNA damage are probably stronger in the germ line than in the somatic line, since damage in DNA that is passed on to descendants will tend to have more serious consequences for genetic survival than damage in somatic-cell DNA. It has recently been proposed that an important function of sexual reproduction is to provide a special opportunity for recombinational repair of germ-line DNA through the pairing of homologous chromosomes (see Bernstein et al. 1981 and references therein). This pairing may allow a damaged DNA sequence in one chromosome to be restored through physical exchange of DNA (recombination) with another homologous chromosome. In addition to its probable role in sexual reproduction, recombinational repair seems to be an important mechanism for dealing with DNA damage in vegetatively growing bacteria and fungi. In experiments investigators usually infer that recombinational repair has occurred if, after treatment of an organism with a DNA-damaging agent, the viability of the treated organism and/or the restoration of the integrity of its damaged DNA can be shown to depend on the presence of more than one copy of a chromosome and gene functions needed for genetic recombination. This paper reviews experimental information on recombinational repair in the various organisms that have been studied, on the range of organisms that use recombinational repair, on the variety of lesions against which it acts, and on its efficiency in overcoming DNA damage. This evidence supports the hypothesis that recombinational repair is a major function of sexual reproduction.