Quantitative PCR analyses. Total RNAs from erythroid tissues were amplified for detection of μ-globin (A) and α-globin (B). One million copies of DNA encoding α-globin (α clone) and μ-globin (μ clone) were included as negative controls to demonstrate specificity. Also shown is a comparison of μ-globin (C) and α-globin (D) expression levels in differentiating erythroblasts during culture (14 days) of CD34⁺ cells in erythropoietin (culture day on x-axis). All studies were performed in triplicate. Copy numbers were calculated by standard curve comparison. Mean values and standard deviation bars are shown. Asterisks indicate a significant change (t test; P < .001) compared with no significant (N.S.) change between fetal and adult erythroid tissues. For abbreviations, see the legend to Figure 3.