The defect sickle - cell anaemia is caused by the ________ of glutamic acid by valine at the 6th 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, we need to fill in the blanks regarding sickle-cell anemia and its genetic basis. Here’s the step-by-step solution:

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

2. **Understand the Mutation**: Sickle-cell anemia is caused by a specific mutation in the hemoglobin gene. This mutation involves the substitution of one amino acid for another in the hemoglobin protein.

3. **Locate the Amino Acid Change**: The mutation specifically involves the substitution of glutamic acid with valine at the 6th position of the hemoglobin chain.

4. **Identify the Type of Globin Chain**: The hemoglobin molecule consists of different globin chains, including alpha and beta globin chains. The mutation causing sickle-cell anemia occurs in the beta-globin chain.

5. **Fill in the Blanks**: Based on the information gathered:
- The first blank is "substitution" (the defect is caused by the substitution of glutamic acid by valine).
- The second blank is "beta" (the mutation occurs at the 6th position of the beta globin chain).

Thus, the completed sentence is: "The defect sickle-cell anaemia is caused by the **substitution** of glutamic acid by valine at the 6th position of the **beta** globin chain of the haemoglobin molecule."