A, Length of the cell cycle in lineage-negative c-kit-positive hCSCs. Mean±SD. The sequence of the phases of the cell cycle, i.e., G2, S, and G1, reflects the order in which cells enter mitosis after the BrdU pulse. Cells in G2 are the first to reach mitosis; these cells, however, are BrdU-negative. Subsequently, cells that are in S phase will divide and the mitotic figures will be BrdU-positive, deflecting upwards the labeled mitosis curve. Finally, cells in G1 at the time of the BrdU pulse will reach mitosis; they will be BrdU negative and mitotic figures will be no longer labeled by the thymidine analog. B, Lineage-negative c-kit-positive hCSCs (green) are BrdU-positive (white) before plating for clonal analysis. C, Individual lineage-negative c-kit-positive hCSCs (green) were plated at limiting dilution (left panel), or seeded in single wells of Terasaki plates (right panel). BrdU, white. D, Clonal efficiency in each sample is shown together with the mean±SD.