Final answer:
In homologous recombination, a single-stranded piece of DNA is generated through exonuclease activity that trims back the damaged DNA. RecA protein then facilitates the search for a homologous sequence and strand invasion for accurate repair. This process is central to DNA repair mechanisms and is also pivotal in meiosis for increasing genetic diversity through crossover events.
Step-by-step explanation:
Generation of Single-Stranded DNA in Homologous Recombination
In homologous recombination, the generation of a single-stranded piece of DNA is a critical step for the repair of both single-stranded and double-stranded breaks. When a replication fork encounters damage to one strand of DNA, a 5'-3' exonuclease begins the repair by trimming the damaged DNA. After this, the RecA protein binds to the single-stranded DNA forming a nucleoprotein filament. This filament then scans the complementary strand for a homologous sequence to bind to. Upon finding a match, strand invasion occurs, and the repairing DNA strand pairs with its homologous counterpart. The damaged DNA strand is then extended from the 3' end of the invading single strand, leading to the precise and accurate repair of the original break without loss or insertion of genetic material.
During meiosis, homologous recombination is essential for genetic diversity. It involves the breakage and rejoining of DNA between non-sister chromatids at sites called recombination nodules on the synaptonemal complex. This leads to crossover events, which are a hallmark of meiosis I, contributing to the genetic variation in gametes. Recombination nodules facilitate the process by cleaving the DNA, allowing for the exchange and then ligation of DNA between homologs.