In sickle cell anemia defect is in which chain?
**Core Concept**
Sickle cell anemia is a genetic disorder caused by a mutation in the hemoglobin gene, leading to the production of abnormal hemoglobin that causes red blood cells to become misshapen and sickle-shaped. This mutation affects the structure of the hemoglobin protein, specifically the globin chains.
**Why the Correct Answer is Right**
The defect in sickle cell anemia is a point mutation in the HBB gene that codes for the beta-globin chain of hemoglobin. This mutation leads to the substitution of glutamic acid with valine at position 6 of the beta-globin chain, resulting in the production of sickle hemoglobin (HbS). The abnormal beta-globin chains aggregate and cause polymerization, leading to the characteristic sickling of red blood cells.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because the defect in sickle cell anemia is not in the alpha-globin chain, which is encoded by the HBA1 and HBA2 genes.
**Option B:** This option is incorrect because the defect in sickle cell anemia is not in the gamma-globin chain, which is a precursor to beta-globin and is encoded by the HBB gene.
**Option C:** This option is incorrect because the defect in sickle cell anemia is not in the delta-globin chain, which is a minor component of adult hemoglobin and is encoded by the HBD gene.
**Clinical Pearl / High-Yield Fact**
The sickle cell trait, which is a carrier state for the sickle cell gene, can be identified by a hemoglobin electrophoresis test. Individuals with the sickle cell trait do not typically exhibit symptoms of sickle cell anemia, but they can transmit the mutated gene to their offspring.
**Correct Answer:** D.