Defect leading to thalassemia lies in –
**Core Concept**
Thalassemia is a genetic disorder affecting hemoglobin production, characterized by reduced or absent production of one or more globin chains. It is a result of mutations in the genes encoding the alpha (α) or beta (β) globin subunits of hemoglobin.
**Why the Correct Answer is Right**
The correct answer is related to the mutation in the HBB gene, which encodes the beta-globin subunit of hemoglobin. Thalassemia major, also known as Cooley's anemia, is caused by a mutation in the HBB gene that leads to the production of a truncated or non-functional beta-globin protein. This results in a significant reduction in the production of the beta-globin chains, leading to severe anemia. The HBB gene mutation is located on chromosome 11.
**Why Each Wrong Option is Incorrect**
**Option A:** Incorrect because the HBA2 gene encodes the alpha-2 globin subunit, not the beta-globin subunit.
**Option B:** Incorrect because the HBA1 gene encodes the alpha-1 globin subunit, not the beta-globin subunit.
**Option C:** Incorrect because the HBA1 and HBA2 genes are responsible for alpha-thalassemia, not beta-thalassemia.
**Clinical Pearl / High-Yield Fact**
Thalassemia is a genetic disorder that is more common in individuals of Mediterranean, Middle Eastern, and South Asian descent. It is essential for clinicians to recognize the signs and symptoms of thalassemia, including severe anemia, jaundice, and bone deformities.
**Correct Answer:** D.