The timeline of the expression of the human globin genes from early stages of fetal development to the changes that occur at birth and in the first year of life. Also shown are the major sites of erythropoiesis and the types of hemoglobin-containing cells during these periods. These analyses are largely based on observations of clinical samples made by Huehns et al in the 1960s; the figure is reprinted from Wood (Br Med Bull. 1976;32:282) with permission. Illustration by Alice Y. Chen.