The human beta globin gene cluster located on chromosome 11 spans about 45 kb and includes 5 functional genes and 1 pseudogene. The order of genes is: 5'-epsilon, gamma G, gamma A, beta 1 pseudogene, delta, beta -3'.

These beta-like genes have the same overall exonic structure, leading to the conclusion that they are derived from one ancestral gene. The epsilon and the 2 gamma globin genes are expressed in early embryonic and fetal erythroid tissues, while delta and beta globin genes are expressed in adult life.

Two epsilon chains combine with two zeta chains to constitute the emryonic hemoglobin Hb Gower I; two epsilon chains together with two alpha chains form the embryonic Hb Gower II; two epsilon chains together with two alpha chains to make fetal hemoglobin HbF. T

wo gamma chains combine two alpha chains to make fetal hemoglobin HbF. And, two alpha chains plus two beta chains constitute HbA, which in normal adult life comprises about 97% of the total hemoglobin. Sickle cell anemia and beta thalassemia result from mutation and absence, respectively, of beta globin chain.