The defect sickle-cell anaemia is caused by the `"_____"` of glutamic acid by the valine at the `6^(th)` position of the `"_____"` globin chain of the haemoglobin molecule.

Options

A. Substitution, `beta`
B. Deletion, `alpha`
C. Duplication, `beta`
D. Translocation , `alpha`

Answer

To solve the question regarding sickle-cell anemia, we can break it down into the following steps:

### Step-by-Step Solution:

1. **Understanding Sickle-Cell Anemia**:
- Sickle-cell anemia is a genetic disorder that affects the hemoglobin in red blood cells, causing them to assume a sickle shape instead of the normal biconcave shape.

2. **Identifying the Mutation**:
- The disorder is caused by a specific mutation in the hemoglobin gene. This mutation leads to the production of abnormal hemoglobin.

3. **Locating the Position of Mutation**:
- The mutation occurs at the 6th position of the beta globin chain of hemoglobin.

4. **Identifying the Amino Acids Involved**:
- In normal hemoglobin, the amino acid present at the 6th position is glutamic acid. In sickle-cell anemia, this glutamic acid is replaced by valine.

5. **Filling in the Blanks**:
- Therefore, the correct answer to the question is:
- The defect sickle-cell anemia is caused by the **substitution** of glutamic acid by the valine at the **6th** position of the **beta** globin chain of the hemoglobin molecule.

### Final Answer:
The defect sickle-cell anaemia is caused by the **substitution** of glutamic acid by the valine at the **6th** position of the **beta** globin chain of the haemoglobin molecule.

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