Partitioning of p27-expressing and p21-expressing cells within the cell cycle. Cord blood CD34⁺ cells differentiated for 5 days were analyzed simultaneously for p27 expression and cell-cycle distribution (left) or for p21 expression and cell-cycle distribution (right). Ninety-three percent of cells were positive and 7% were negative for p27. Sixty-one percent of cells were positive and 39% were negative for p21. Isotype gates and representation of cellular populations are as in Fig 10. p27 (left) and p21 (right)-negative cells at bottom; p27 (left) and p21 (right)-positive cells in middle. As is evident, the cell-cycle profile of cdki-positive and -negative cells is similar.