Schematic representation of the critical steps of homologous recombination. The early steps of the reaction consist of processing the substrate DNA. Indicated in red is a DNA molecule with a double-stranded break. The DNA ends are processed to form 3' single-stranded tails. During the middle steps, the tails are used by Rad51 and its accessory proteins to search for, and invade, a homologous DNA template (green). In the resulting joint molecules, extension and annealing of DNA strands by de novo synthesis (blue) restores the continuity of the broken DNA. During the late steps, the branched Holliday junctions are resolved into two duplex DNAs. For simplicity, only one outcome of the resolution process is shown.