Flow cytometric analyses of HbF and HbA expression during postnatal development. Representative flow cytometric histograms from (A) umbilical cord blood, (B-G) blood from infants of ages 1 to 6 months, respectively, and (H) adult blood. Cells were dual stained with anti-HbF and anti-HbA antibodies. Thirty thousand cells were analyzed for each sample. Left panels show histogram analyses of HbF expression (x-axis) versus the cell count (y-axis). Center panels show scatterplot analyses with HbF fluorescence (x-axis) versus HbA fluorescence (y-axis). The percentage of HbF-silenced cells is shown in the top left of each center panel. Right panels provide a 3-dimensional, density view of the data shown in the middle panels. The vertical axis represents the cell count at each level of HbF and HbA fluorescence. The HbF and HbA coordinates with cells are shown as peaks with arbitrarily assigned colors (red-colored peaks denote the highest densities of cells). Bars shown in left and center panels denote the upper level of fluorescence among 98% of cells stained with the isotypic controls.