Homologous recombination is a type of genetic recombination in which nucleotide sequences are exchanged between two similar or identical molecules of DNA. It is most widely used by cells to accurately repair harmful breaks that occur on both strands of DNA, known as double-strand breaks. Homologous recombination also produces new combinations of DNA sequences during meiosis, the process by which eukaryotes like animals and many plants make sperm and egg cells. These new combinations of DNA represent genetic variation in offspring, which in turn enables populations to adapt during the course of evolution. Homologous recombination is also used in horizontal gene transfer to exchange genetic material between different strains and species of bacteria and viruses.
The HRR pathway is an "error free" DNA repair mechanism that utilizes information encoded by homologous sequence to repair double-strand breaks (DSBs). HRR acts on DSBs occurring within replicated DNA (replication-independent DSBs) or on DSBs that are generated at broken replication forks (replication-dependent DSBs). Repair by homologous recombination involves processing of the ends of the DNA double-strand break, homologous DNA pairing and strand exchange, repair DNA synthesis, and resolution of the heteroduplex molecules.