(a) In vitro differentiated erythroid colonies of EKLF+/+, EKLF+/−, and EKLF−/− ES cell-derived erythroid colonies at day 8 of replating. Both EKLF+/+ and EKLF+/− colonies were hemoglobinized as indicated by the reddish coloration, whereas the EKLF−/− colony was poorly hemoglobinized with a slight reddish tinge. Colonies are shown at the same magnification. (b) Staining of EKLF+/+ and EKLF−/− colonies with crystal violet. Single colonies were picked, spread on slides, and stained with crystal violet. Small dark Heinz bodies indicative of excess α-globin chains were present in the enucleated EKLF−/− erythrocytes (N, nucleus; E, erythrocytes).