Sox6^–/– mice show abnormal development of erythropoietic tissues. (A) CD71/TER119 FACS profiles of control and Sox6^–/– erythropoietic tissues during their first wave of erythropoiesis. Four subpopulations are distinguished: CD71^neg/lowTER119^– early erythroid and nonerythroid cells; CD71^med/highTER119^low proerythroblasts; CD71^highTER119⁺ early erythroblasts; and CD71^med-lowTER119⁺ late erythroblasts. The percentage of cells in each subpopulation is indicated. (B) CD71/TER119 FACS profiles of erythropoietic tissues beyond their first wave of erythropoiesis. (C) Pictures and weight of representative newborn control and mutant mouse livers. All mice had similar body weight.