Summary of changes in relative globin mRNA levels, normalized to 18S rRNA, as primitive erythroid cells mature from proerythroblasts at E7.5 to E8.5 to reticulocytes at E15.5 in the mouse. The E7.5 and E8.5 values are based on dissected yolk sac tissues, E10.5 on whole peripheral blood, and E12.5 and E15.5 values on sorted cell populations. (A) Levels of total α-globin and β-globin gene transcripts quantified by qPCR suggest that total α-globin transcripts accumulate in excess of β-globin transcripts. (B) Relative levels of ϵy-, βH1-, and β1-globin transcripts reveal the βH1- to ϵy-globin switch between E8.5 and E12.5. (C) Relative levels of the ζ- and α1/α2-globin transcripts reveal the predominance of α1/α2-globin gene from the earliest stages of primitive erythroid maturation. Error bars represent SEM.