Temporally uncoupled signal and coding joint formation in human V(D)J recombination

•The cellular efficiency of signal relative to coding end joining in V(D)J recombination is not known.•ddPCR permits independent analysis of signal (SJ) and coding joints (CJ) on inversion substrates.•SJ and CJ formation are temporally uncoupled such that one joint can often remain incomplete when the other has formed.•Despite their temporal gap, the overall ratio of SJ/CJ is close to 1 in a human pre-B cell line.