Developmental pattern of γ-globin expression in the single copy mouse lines. (A) S1 nuclease protection analysis of human ^Aγ gene expression versus mouse βmaj in fetal liver RNA from day-12.5 and day-16.5 embryos and in adult blood RNA (bld) of the single copy transgenic lines. The protected fragments are indicated to the left of the panel. The specific activity of the βmaj probe was 2.35 times that of the γ probe. (B) Quantitation of γ-globin expression levels of the single copy lines shown in panel A, as a percentage of βmaj expression per copy.