Dot plot and single parameter histograms of a typical Hoechst 33342 (X axis) and Pyronin Y (Y axis) staining of bone marrow CD34⁺ cells. CD34⁺ cells were first sorted to homogeneity, then stained with Hst and PY as described in Materials and Methods. The single parameter histograms are shown here to elucidate the contribution of each stain to the formation of the dot plot. The DNA/RNA staining shown in this figure was derived from a cultured (7 days with SCF, IL-3, and IL-6) BM sample of CD34⁺ cells to elaborate the S/G₂ + M population for better definition of all three phases of cell cycle. Sort windows R1, R2, and R3 shown in the dot plot represent the windows used to collect G₀ , G₁ , and S/G₂ + M cells, respectively. R4 designates the area in such a dot plot where dead cells are located.