Map of the β-globin gene cluster with the 9-kb ‘hotspot’ delineated by the TaqI-5′δ (5′) and theHgiAI-β (3′) sites. RFLP sites are indicated by the arrows. The 4.5-kb fragment encompassing the 5′ flanking β region is amplified using two sets of primers: 5′R3K versus 3′R5K and 5′β422 and 3′β9. The other polymorphic sites are indicated by vertical lines. The pur, chi, and the 21-bp element at position −355021 are represented by thick horizontal lines. The crossover regions and the region of initiation replication (IR) are indicated below. A total of 11 and 14 primers were used to sequence the forward and reverse strand of the 4.5-kb region, respectively. The sequences and locations of these primers are available on request.