Sickle cell-anaemia disorder arises due to

Options

A. Duplication of a segment of DNA
B. Substitution in a single base of DNA
C. Deletion of a segment of DNA
D. Duplication in a base pair of RNA

Answer

### Step-by-Step Solution:

1. **Understanding Sickle Cell Anemia**:
- Sickle cell anemia is a blood disorder characterized by the abnormal shape of red blood cells (RBCs). Instead of the normal disc shape, the RBCs become rigid and take on a sickle or crescent shape.

2. **Effects of the Abnormal Shape**:
- The sickle-shaped RBCs are sticky and can clump together, leading to blockages in blood vessels. This results in reduced blood flow and oxygen transport throughout the body, causing various health complications.

3. **Cause of Sickle Cell Anemia**:
- The disorder arises due to a genetic mutation. Specifically, it is caused by a single nucleotide substitution in the DNA sequence that codes for hemoglobin, the protein in RBCs responsible for oxygen transport.

4. **Understanding the Mutation**:
- In normal hemoglobin, a specific codon codes for the amino acid glutamic acid. However, in sickle cell anemia, there is a substitution where one base is changed (for example, adenine (A) is replaced by thymine (T)). This change alters the codon, leading to the incorporation of valine instead of glutamic acid in the hemoglobin protein.

5. **Resulting Protein Change**:
- The altered hemoglobin (known as hemoglobin S) causes the red blood cells to deform into the sickle shape. This mutant protein is responsible for the symptoms and complications associated with sickle cell anemia.

6. **Conclusion**:
- Therefore, sickle cell anemia arises due to a substitution in a single base of DNA, which leads to the production of a mutant form of hemoglobin.

### Final Answer:
Sickle cell anemia disorder arises due to a substitution in a single base of DNA.

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