Disease classification is based on the number and location of deletions: Alpha + thalassemia: Loss of a single gene on one chromosome (alpha / - -) Alpha 0 thalassemia: Loss of both genes on the same chromosome (- - / - -) Beta-thalassemia Beta-thalassemia results from decreased production of beta-polypeptide chains due to either mutations or deletions in the beta globin gene, leading to impaired production of hemoglobin (Hb) A Mutations or deletions may result in partial loss (beta + allele) or complete loss (beta 0 allele) of beta globin function.