Maturational globin gene switching in developing primitive erythroid cells. “Maturational” globin gene switching⁴⁰  refers to sequential changes in expression from βh1- to εY- (both embryonic) to adult βmaj- (β1) globin within the primitive erythroid lineage during its differentiation. (A) Relative expression is shown for the 3 β-like globin genes. εY-globin remains the predominant transcript throughout EryP development; even at late times, βmaj-globin expression remains low. (B) The data are presented in a normalized form, with peak expression set at 100 for each gene, to emphasize their sequential expression within maturing EryP from E8.5 to E12.5 (J.I., Z. He, M.H.B., unpublished data, February 2009).