To avoid unwarranted negative selection during the introduction of the “rival” oncogene (i.e. NRAS(Q61) for BRAF(V600E) melanoma lines and BRAF(V600E) for NRAS(Q61) melanoma lines), we used a Tet-On system to synchronize expression of the second allele in a panel of four isogeneic stable NRAS(Q61R/K) + doxycycline-induced Tet-On- BRAF(V600E) lines (designated as “NRAS* + iBRAF*”) and five BRAF(V600E) + doxycycline-induced Tet-On-NRAS(Q61R) lines (designated as “BRAF* + iNRAS*”) (Fig. 1a) along with an immortalized primary human melanocyte line (Pmel). The gene discussed is NRAS; the disease is melanoma.