Total number of stem and progenitor cells and of maturing erythroblasts in normal as well as in hemizygous Gata1^low mutants of different background, as indicated. C57BL/6 mutants were not analyzed because they were never born. The total number of each cell population was calculated by multiplying its frequency (Table 4) per the total number of cells per organ (Table 1), taking into account that the cells in a femur correspond to 8% of the total marrow population of a mouse.⁷⁴  The relative contribution of the marrow, spleen, and liver to each population is indicated in black, gray, and white, respectively.