The primary pathways for repairing DSBs are homologous recombination (HR) and non-homologous end joining (NHEJ). HR is a high-fidelity process that uses a sister chromatid as a template to accurately repair the break. This pathway is active during the S and G2 phases of the cell cycle. In contrast, NHEJ is more error-prone and involves direct ligation of the broken DNA ends without the need for a template. NHEJ is active throughout the cell cycle but is particularly crucial during the G1 phase.
