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Genetic recombination is a complex process that involves alignment of two homologous DNA strands, precise breakage of each strand, equal exchange of DNA segments between the two strands, and sealing of the resultant recombined DNA molecules through the action of enzymes called ligases. Despite the complexity of this process, recombination events occur with remarkable accuracy and precision in the vast majority of instances.
Beyond its role in meiosis, recombination is important to somatic cells in eukaryotes because it can be used to help repair broken DNA, even when the break involves both strands of the double helix. These breaks are known as double-stranded breaks, or DSBs. When DSBs happen, a homologous chromosome can serve as the template for synthesis of whatever portion of the genetic material has been lost as a result of the break. Then, once synthesized, this new DNA can be incorporated into the broken DNA strand, thereby repairing it. In effect, this is a form of recombination, because the broken-off area is replaced with new material from a homologous chromosome. Recombination can also be used in a similar way to repair smaller, single-stranded breaks. In general, recombination can occur any time homologous chromosomes pair up, whether they are freely floating in tandem or lined up on the metaphase plate during meiosis.
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