Homology directed repair (HDR) through homologous recombination is known as homologous recombination repair (HRR). HRR occurs after extensive resection of DNA double strand break (DSB) ends, which creates long 3'-ssDNA overhangs. RAD51 coats 3'-ssDNA overhangs in a BRCA2-controlled fashion, creating invasive RAD51 nucleofilaments. The RAD51 nucleofilament invades a sister chromatid DNA duplex, leading to D-loop formation. After the D-loop is extended by DNA repair synthesis, the resulting recombination intermediates in the form of extended D-loops or double Holliday junctions can be resolved through crossover- or non-crossover-generating processes (reviewed by Ciccia and Elledge 2010).