Homologous recombination

Homologous recombination is the exchange of DNA strands between molecules with similar or identical sequences. It repairs DNA breaks using a matching template and reshuffles genetic material during meiosis.

Double-strand break: A DNA lesion in which both strands of the double helix are severed. A major trigger for recombination-based repair is a break that must be rebuilt from an intact template.
DNA double helix: The paired, helical structure formed by two complementary DNA strands. Complementary base pairing lets an intact duplex serve as a repair template.
Meiosis: A cell division process that produces haploid cells through one round of DNA replication and two rounds of chromosome segregation. Recombination between homologous chromosomes helps pair them and creates genetic variation.
Non-homologous end joining: A DNA repair pathway that rejoins broken DNA ends without requiring an extensive homologous template. Unlike homologous recombination, it can operate without a matching DNA molecule but often introduces small mutations.
End resection: The processing of broken DNA ends to expose single-stranded DNA, usually with a 3′ overhang. Resection creates the single-stranded substrate that searches for matching DNA.
DNA mismatch repair: A pathway that detects and corrects incorrectly paired bases and small insertion or deletion loops in DNA. Mismatch repair helps distinguish closely related sequences and can limit exchanges between diverged DNA.
Gene conversion: A nonreciprocal transfer of sequence information between homologous DNA molecules during repair or recombination. Template-directed repair can copy one allele's sequence into another without a reciprocal swap.
Alternative end joining: A family of backup DNA break repair pathways that join ends using short sequence matches or other end-processing mechanisms. These pathways compete with homology-based repair and can create deletions or rearrangements.
RAD51: A recombinase protein that assembles on single-stranded DNA and promotes homology search and strand invasion in eukaryotes. RAD51 coats the exposed DNA and drives the central strand-invasion step.
Homology search: The process by which a single-stranded DNA region locates a complementary sequence within another DNA molecule. Recombination requires finding the matching template before strand invasion can proceed.

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