Representative double-labeled FITC-CD71 and PE-TER119 histoplots from E9.5 blood. Flow cytometry was used to determine CD71 and TER119 staining intensity of blood cells from E9.5 yolk sac and embryos. Mean percentages plus or minus standard deviations are indicated in each gate R1-R5 for each genotype. Regions R1 through R5 are defined respectively as CD71^medTER119^low, CD71^highTER119^low, CD71^highTER119^high, CD71^medTER119^high, and CD71^lowTER119^high. R1 contains predominantly progenitor cells, R2 contains proerythroblasts and early basophilic erythroblasts, R3 has early and late basophilic erythroblasts, R4 has chromatophilic and orthochromatophilic erythroblasts, and R5 has late orthochromatophilic erythroblasts and reticulocytes.²⁵  (A) Wild type, mean percentages calculated from n = 32 embryos. (B) KLF2^−/−, n = 8. (C) EKLF^−/−, n = 10. (D) EKLF^−/−KLF2^−/−, n = 8.