The developmental change in the G gamma and A gamma globin. Proportions in hemoglobin F

The proportions of G gamma and A gamma globins in hemoglobin F were determined in fetuses around the 20th week of gestation, newborns, and children 3 weeks to 5 months of age. In the last group, the G gamma/G gamma + A gamma ratio decreased continously; there was a good correlation between the decline of G gamma with respect to total gamma and the decline of Hb F (r = 0.88). In contrast, there was virtually no difference in the gamma globin composition of Hb F between the fetuses and the newborns, i.e. in late pregnancy, the decrease in the synthesis of both gamma globins appears to be proportionate. The G gamma and A gamma globin genes may be inactivated in a sigmoidal fashion with time, thus producing a G gamma/G gamma + A gamma ratio which at first changes only slightly and then declines linearily.