Sickle - cell anemia trait is adaptation against malaria. It is due to substitution ( point mutation ) in which

Options

A. instead of an acidic amino acid valine , a neutral amino acid valine comes at the number `6^th` position in one of the `beta` - chain of Hb
B. instead of neutral amino acid valine, acidic amino acid glutamic acid is inserted at the number `6^(th)` position of `beta` chain Hb
C. instead of neutral amino acid glutamic acid , an acidic amino acid valine comes at `6^(th)` position in one of the `beta` - chain of Hb
D. instead of an acidic amino acid glutamic acid , a neutral amino acid valine comes at `6^(th)` position in one of the `beta` - chain of Hb

Answer

**Step-by-Step Solution:**

1. **Understanding Sickle Cell Anemia**: Sickle cell anemia is a genetic disorder caused by a mutation in the hemoglobin gene. This mutation leads to the production of abnormal hemoglobin, known as hemoglobin S (HbS), which causes red blood cells to become rigid and sickle-shaped.

2. **Identifying the Mutation**: The specific mutation responsible for sickle cell anemia is a point mutation, which is a change in a single nucleotide in the DNA sequence of the hemoglobin gene. In this case, the mutation occurs in the codon that codes for the amino acid in the beta-globin chain of hemoglobin.

3. **Analyzing the Codon Change**: The normal codon for the amino acid glutamic acid is GAG. In sickle cell anemia, this codon is mutated to GTG (or GUG), which codes for the amino acid valine. This change from glutamic acid (an acidic amino acid) to valine (a neutral amino acid) is crucial in the pathology of sickle cell anemia.

4. **Conclusion**: Therefore, the substitution point mutation in sickle cell anemia results in the replacement of an acidic amino acid (glutamic acid) with a neutral amino acid (valine). This mutation provides a selective advantage against malaria, as individuals with the sickle cell trait are more resistant to the malaria parasite.

5. **Final Answer**: The correct option is D: "instead of an acidic amino acid (glutamic acid), a neutral amino acid (valine)".

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