To determine the differential growth speed of each cell subpopulation in vivo, we extracted DNA from the right hemisphere of each mouse's brain in which the pre-mixed 51A-GFP and 51B-RFP cells had been implanted and developed into a tumor, and performed CQ-PCR to quantify the copy numbers of GFP, RFP, EGFR and SPAG16 on DNA of 3-4 mice per group. The gene discussed is EGFR; the disease is neoplasm.