Sickle-cell anaemia is caused due to the substitution of :

Options

A. Valine by glutamic acid at sixth position of alpha chain of heamoglobin
B. Valine by glutamic acid at sicth position of beta chain of haemoglobin
C. glutamic acid by valine at sixth position of alpha chain of haemoglobin
D. glutamic acid by valine at sixth position of deta chain of haemoglobin

Answer

### Step-by-Step Solution:

1. **Understanding Sickle-Cell Anemia**: Sickle-cell anemia is a genetic disorder that affects the structure of hemoglobin, which is the protein in red blood cells (RBCs) responsible for transporting oxygen.

2. **Identifying the Mutation**: The disorder is caused by a mutation in the gene that encodes the beta chain of hemoglobin. This mutation is a specific type of substitution mutation.

3. **Analyzing the Amino Acid Sequence**: In normal hemoglobin, the sixth amino acid in the beta chain is glutamic acid. This amino acid is coded by the codon GAG.

4. **Identifying the Substitution**: In sickle-cell anemia, a mutation occurs where the codon GAG (which codes for glutamic acid) is replaced by GTG (which codes for valine). This results in the substitution of glutamic acid with valine at the sixth position of the beta chain.

5. **Conclusion**: Therefore, sickle-cell anemia is caused by the substitution of glutamic acid with valine at the sixth position of the beta chain of hemoglobin.

### Final Answer:
Sickle-cell anemia is caused due to the substitution of glutamic acid by valine at the sixth position of the beta chain of hemoglobin.

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