The dHJ pathway but differs in some of the details of the replicative steps. Both mechanisms occur when the two ends of the resected DSB are homologous to the intact DNA molecule. The major difference is that in SDSA the extension of the first strand by RDR occurs within a translocating D-loop (Figure 1B, Step 1). As DNA synthesis extends the first strand at the leading edge of the D-loop, the fir