Alpha and beta globin gene clusters

Schematic representation of the human beta globin gene cluster on chromosome 11 (upper panel) and alpha globin gene cluster on chromosome 16 (lower panel). These illustrate the relative positions of the globin genes, the locus control region (LCR) for the beta globin gene cluster, consisting of hypersensitive sites for the beta globin gene cluster (HS-1 to 5) and the alpha gene cluster (HS-40). Before birth, the most active genes in the beta globin gene cluster are those for Gγ (G-gamma; HBG2 gene), and Aγ (A-gamma; HBG1 gene). After birth, the most active genes are δ (delta) and β (beta) globin. The genes active before and after birth in the alpha globin gene cluster are α2 (alpha-2) and α1 (alpha-1). Shown between the two panels is hemoglobin F (Hb F; fetal hemoglobin), a tetramer or two gamma globin chains and two alpha globin chains, and hemoglobin A (Hb A; adult hemoglobin), a tetramer of two beta globin chains and two alpha globin chains. The ε (epsilon) and ζ (zeta) genes encode embryonic hemoglobins that are not produced after birth. The pseudo-genes (labeled below the corresponding boxes) are not transcribed.