RNA samples prepared from blood of staged fetuses and adults were assayed by RPA as described. On the y-axis, expression of each human globin gene is displayed as a percentage of total globin transcribed. The developmental days post-conception are shown on the x-axis. Experimental values for the Δ5’HS4 lines are the means and standard deviations of all three lines with a minimum of two conceptuses for each line at each time point from 3 independent experiments. Standard deviations are not shown for the wild-type β-YAC data, so that the data in the figure would not be difficult to read; the mean values plotted are derived from 3 independent experiments, with duplicate samples for each time point in each experiment. The mean values plotted are well within norms of our previously published reports using this line. Note the longer switching period observed in the Δ5’HS4 lines. Open symbols, wild-type β-YAC line 26223; closed symbols, Δ5’HS4 β-YAC lines. Diamonds, ε-globin; triangles, γ-globin; squares, β-globin.