Which pattern corresponds to one defective beta-globin gene in beta-thalassemia?

• A. Thalassemia major
• B. Thalassemia minor
• C. Thalassemia intermedia
• D. Sickle cell disease

Answer: (B)

Having one defective beta-globin gene means you’re heterozygous for beta-thalassemia, producing a mild form known as thalassemia minor (thalassemia trait). In this state, there’s enough beta-globin production to prevent severe symptoms, so people often have only mild, microcytic anemia or may be asymptomatic. The condition is a carrier state, and many individuals are diagnosed only on routine blood tests or family studies.

In contrast, beta-thalassemia major occurs when both beta-globin genes are severely defective, leading to little or no beta-globin production and severe anemia in early childhood. Beta-thalassemia intermedia is more variable and reflects partial beta-globin production or milder mutations, resulting in a spectrum between minor and major. Sickle cell disease involves a mutation in the beta-globin gene that produces hemoglobin S; disease typically arises when two abnormal beta-globin alleles are present (such as HbSS or HbS with a beta-thalassemia allele), not from a single defective beta-globin gene.