Introduction : Heterogenesity in the clinical manifestations of beta thalassemias may occur from the type & nature of the beta globin gene mutation itself ,alpha thalassemia gene interaction, and presence of Xmn-1 polymorphic site.Material & methods : 32 cases of beta thalassemia were screened for the common Mediterranean mutations, α-gene deletions, and presence of gamma G ,Xmn-1 polymorphic site.Results: clarified that co-inheritance of α-thalassemia 4/32 alleviated the severity of beta thalassemia ; silent,mild and severe β-thalassemic alleles ;& DNA polymorphism at – 158 (C – T ) of gamma glycine gene was demonstrated in 2/32 with high HbF.