**4.2 Beta (β) globin gene cluster**

The β-globin gene cluster is located along a 60-kb segment of the short arm of chromosome 11 (11p15.5) and contains five functional genes (β, δ, <sup>G</sup>γ, <sup>A</sup>γ, and ε) and one pseudogene (**Figure 3**). The genes are arranged in the order in which they are expressed during different developmental stages [21]. The regulatory sequences contain four (HS-1 to HS-5) erythroid specific DNAse hypersensitive sites (HSs) known as locus control region (LCR), which is required for DNA-protein interaction. The *HBB* gene, spans about 1.6 Kb, contains three exons (coding regions) and two introns with 5'and 3'untranslated regions (UTRs). The HBB gene, spans about
