The order of the genes in the beta-globin cluster is 5' - epsilon – gamma-G – gamma-A – delta – beta - 3'.

Beta thalassemia minor results in a mild microcytic anemia that is often asymptomatic or may cause fatigue and or pale skin.

[14] Beta thalassemia major can be treated by lifelong blood transfusions or bone marrow transplantation.

HbS is produced by a point mutation in HBB in which the codon GAG is replaced by GTG.

[22] Another point mutation in HBB, in which glutamic acid is replaced with lysine at position 26 (β26Glu→Lys), leads to the formation of haemoglobin E (HbE).

Even though the unstable protein itself has mild effect, inherited with HbS and thalassemia traits, it turns into a life-threatening form of β-thalassemia.

[24] Malaria due to Plasmodium falciparum is a major selective factor in human evolution.

[26][27] For example, there is evidence that the sickle cell mutation, common in people of African descent, provides a degree of resistance to severe malaria.

[28] Thus, HBB mutations are the sources of positive selection in these regions and are important for their long-term survival.