Description
The delta (HBD) and beta (HBB) genes are normally expressed in the adult: two alpha chains plus two beta chains constitute HbA, which in normal adult life comprises about 97% of the total hemoglobin. Two alpha chains plus two delta chains constitute HbA-2, which with HbF comprises the remaining 3% of adult hemoglobin. Five beta-like globin genes are found within a 45 kb cluster on chromosome 11 in the following order: 5′-epsilon–Ggamma–Agamma–delta–beta-3′. Mutations in the delta-globin gene are associated with beta-thalassemia.