In sickle - cell anaemia , the defect is caused by the substitution of ……..(i) ……….by ………(ii) ………..in the ………(iii)………position of the beta - globin chain of the haemoglobin molecule.

Options

A. (i) Val, (ii) Glu , (iii) nineth
B. (i) Glu , (ii) Val , (iii) sixth
C. (i) Val , (ii) Ser , (iii) fifth
D. (i) Gly , (ii) Val , (iii) seventh

Answer

**Step-by-Step Solution:**

1. **Identify the Condition**: The question is about sickle cell anemia, which is a genetic disorder affecting hemoglobin in red blood cells.

2. **Understand the Genetic Basis**: Sickle cell anemia is caused by a specific mutation in the beta-globin gene of hemoglobin. This mutation is a point mutation, meaning it involves a change in a single nucleotide.

3. **Determine the Amino Acid Substitution**: In sickle cell anemia, the amino acid glutamic acid is substituted by valine. This substitution occurs at a specific position in the beta-globin chain.

4. **Identify the Position of Substitution**: The substitution occurs at the 6th position of the beta-globin chain. This is crucial because it is this specific change that leads to the sickling of red blood cells.

5. **Summarize the Information**: Therefore, the defect in sickle cell anemia is caused by the substitution of glutamic acid (i) by valine (ii) in the 6th (iii) position of the beta-globin chain of the hemoglobin molecule.

**Final Answer**:
In sickle-cell anemia, the defect is caused by the substitution of **glutamic acid** (i) by **valine** (ii) in the **6th** (iii) position of the beta-globin chain of the hemoglobin molecule.

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