In Sickle Cell Anaemia defect is in which chain:
**Core Concept**
Sickle Cell Anaemia is a genetic disorder caused by a mutation in the **haemoglobin** gene, leading to abnormal haemoglobin production. This mutation affects the structure and function of haemoglobin, resulting in sickling of red blood cells. The defect is specifically related to the **globin chains** of haemoglobin.
**Why the Correct Answer is Right**
The correct answer is related to the **beta-globin chain**, as the mutation in Sickle Cell Anaemia occurs in the **HBB** gene that codes for the beta-globin subunit of haemoglobin. This mutation leads to the substitution of glutamic acid with valine at position 6 of the beta-globin chain, resulting in **haemoglobin S** (HbS).
**Why Each Wrong Option is Incorrect**
**Option A:** Alpha-globin chain mutations are associated with alpha-thalassemia, not Sickle Cell Anaemia.
**Option C:** Gamma-globin chains are related to fetal haemoglobin, and mutations in these chains are associated with other disorders.
**Clinical Pearl / High-Yield Fact**
Sickle Cell Anaemia is a classic example of a **single-gene disorder** with significant clinical implications, including increased risk of infections, stroke, and organ damage due to sickling of red blood cells.
**Correct Answer:** B. Beta-globin chain.