Radiosensitivity imparted by downregulated CDK4 is not caused by altering cell cycle progression. Cells stably expressing pLKO.1 or shCDK4 were unirradiated (basal), or irradiated at 2 Gy. Then, cells were collected at different times post-irradiation (0, 6, 12, & 24 hours) stained with 7-AAD and were analyzed using flow cytometry to determine the cell cycle stages; 5000 cells per group were analyzed by the flow cytometer. Flow cytometry and analysis was repeated three times. The columns represent the percentage of cells in the G1, S or G2/M phase and presented as average±standard deviation. The G1/S and G2/M graphs were separated in order to make the G2/M data visible.