Schematic of genomic structural organization of the human α-globin and β-globin loci and temporal expression of the various hemoglobin types. The gene order of the α-globin locus on chromosome 16 and the β-globin locus on chromosome 11. Shown at each temporal stage, as indicated on the timeline at bottom, are the types of hemoglobin tetramers produced for each indicated site. LCR indicates locus control region; HbF, fetal hemoglobin; and HbA, adult hemoglobin.