Colonies formed by 1000 untransduced CD71^lo GlyA^lo/- (R1) and CD71⁺ GlyA^int (R2) cells separated by FASC after 6 days in erythroid expansion culture. Cells were plated in semisolid medium containing erythropoietin, IL-3, SCF, and GM-CSF. The cell population in R1 mostly has a CFU-G/GM-forming potential, while R2 contains only cells with an erythroid colony-forming potential. The colony numbers represent 2 separate experiments. Cells in R3 were mature erythroid cells, so colony assays were not performed.