Hemoglobin Alpha 2 (HBa2)

The human alpha globin gene cluster located on chromosome 16 spans about 30 kb and includes seven loci: 5"""- ζ - pseudo ζ - μ - pseudo α1 -α2 -α1 - θ3""". The α2 (HBA2) and α1 (HBA1) coding sequences are identical. These genes differ slightly over the 5""" untranslated regions and the introns, but they differ significantly over the 3""" untranslated regions. Two α-chains plus two-β chains constitute HbA, which in normal adult life comprises about 97% of the total hemoglobin; alpha chains combine with delta chains to constitute HbA-2, which with HbF (fetal hemoglobin) makes up the remaining 3% of adult hemoglobin. Alpha thalassemias result from deletions of each of the alpha genes as well as deletions of both HBA2 and HBA1; some nondeletion alpha thalassemias have also been reported.