DNA And Gene Expression Practice Test

Double-strand break repair that uses a homologous template relies on a nearly identical copy of the sequence to guide restoration, ensuring high accuracy. This process, homologous recombination, first processes the broken ends and then uses a sister chromatid or homologous chromosome as a template. The DNA strand from the template is copied into the break site, and the resulting structures are resolved to restore the original sequence. Because it requires a homologous template, this repair pathway is most active when a sister chromatid is available (during S and G2 phases) and tends to produce error-free repair. In contrast, non-homologous end joining simply ligates the broken ends together without using a template, which can introduce small insertions or deletions. Base excision repair and nucleotide excision repair address different types of DNA damage and do not repair a double-strand break by copying from a homologous template.