Sickle cell anaemia is due to

Options

A. Transition / Base substitution /Point mutation
B. Transversion / Base substitution /Point mutation
C. Transition / Base substitution / Frameshift mutation
D. Transversion / Base substitution / Frameshift mutation

Answer

### Step-by-Step Solution:

1. **Understanding Sickle Cell Anemia**:
- Sickle cell anemia is a genetic disorder that affects the shape and function of red blood cells. In normal conditions, red blood cells are round and flexible, allowing them to move easily through blood vessels. In sickle cell anemia, the red blood cells become rigid and shaped like a sickle or crescent moon.

2. **Identifying the Genetic Basis**:
- The condition is caused by a mutation in the hemoglobin gene. Hemoglobin is the protein in red blood cells that carries oxygen.

3. **Mutation Details**:
- The specific mutation in sickle cell anemia is a point mutation, which is a change in a single nucleotide base pair in the DNA sequence.
- In normal hemoglobin, the DNA sequence includes the codon GAG, which codes for the amino acid glutamic acid.

4. **Base Substitution**:
- In sickle cell anemia, the GAG codon is mutated to GTG (or GUG), which codes for the amino acid valine instead of glutamic acid. This change in one base pair is known as a base substitution.

5. **Type of Mutation**:
- The mutation can be classified as a transversion because it involves the substitution of a purine (adenine, A) with a pyrimidine (uracil, U).
- This is different from a transition mutation, where a purine is replaced by another purine or a pyrimidine is replaced by another pyrimidine.

6. **Conclusion**:
- Therefore, sickle cell anemia is due to a point mutation that results in a base substitution, specifically a transversion, leading to the production of abnormal hemoglobin.

### Final Answer:
Sickle cell anemia is due to a point mutation that results in a base substitution, specifically a transversion, in the hemoglobin gene.

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