The a-globin gene is duplicated on each copy of chromosome 16, so there are a total of four a-globin
genes (two genes per haploid; a1 and a2) in a normal genotype (aa/aa) (Fig. 2). They appear to have a
higher tendency for deletions than most of the mutations affecting the b-globin gene, which frequently
result from one or more nucleotide substitution or deletions. The production of a-globin decreases in
proportion to the number of genes deleted[9,10].