Sickle cell anamia has not been eleiminated from African polulation as

Options

A. It is controlled by dominant genes
B. It is controlled by recessive genes
C. It is not a fatal disease
D. It provides immunity against malaria

Answer

### Step-by-Step Solution:

1. **Understanding Sickle Cell Anemia**:
- Sickle cell anemia is a genetic disorder caused by mutations in the hemoglobin gene. It is hereditary and passed from parents to offspring.

2. **Genetic Basis**:
- The disorder is controlled by two alleles: HBA (normal) and HBS (sickle cell). HBA is dominant while HBS is recessive.
- A person with the genotype HBS HBS is homozygous recessive and suffers from sickle cell anemia.
- A person with the genotype HBA HBA is normal, while HBA HBS is a carrier who does not show symptoms of the disease.

3. **Impact on Red Blood Cells (RBCs)**:
- Normal RBCs are biconcave discs, while those affected by sickle cell anemia take on a sickle shape, which can cause various health issues.

4. **Connection to Malaria**:
- Malaria is caused by a parasite that infects normal RBCs. In individuals with sickle cell anemia, the sickle-shaped RBCs do not provide a suitable environment for the malaria parasite to thrive.

5. **Evaluating the Options**:
- **Option A**: Controlled by dominant genes - Incorrect, as sickle cell anemia is recessive.
- **Option B**: Controlled by recessive genes - While true, it does not explain why it persists in the population.
- **Option C**: Not a fatal disease - Incorrect, as it can be fatal.
- **Option D**: Provides immunity against malaria - Correct, as individuals with sickle cell anemia are less likely to suffer from malaria due to the parasite's inability to thrive in sickle-shaped RBCs.

6. **Conclusion**:
- The reason sickle cell anemia has not been eliminated from the African population is that it provides a selective advantage against malaria, making option D the correct answer.