Genetic recombination is the process by which two DNA molecules exchange genetic information, resulting in the production of a new combination of alleles. In eukaryotes, genetic recombination during meiosis can lead to a novel set of genetic information that can be passed on to progeny. Most recombination is naturally occurring. During meiosis in eukaryotes, genetic recombination involves the pairing of homologous chromosomes. This may be followed by information exchange between the chromosomes. The information exchange may occur without physical exchange; or by the breaking and rejoining of DNA strands, which forms new molecules of DNA. Recombination may also occur during mitosis in eukaryotes where it ordinarily involves the two sister chromosomes formed after chromosomal replication. In this case, new combinations of alleles are not produced since the sister chromosomes are usually identical. In meiosis and mitosis, recombination occurs between similar molecules of DNA. In meiosis, non-sister homologous chromosomes pair with each other so that recombination characteristically occurs between non-sister homologues. In both meiotic and mitotic cells, recombination between homologous chromosomes is a common mechanism used in DNA repair.