Question

Define Point Mutation with the example of Sickle Cell Anemia.

Hint:

Point mutation = Single base change

• Sickle cell: GAG $\rightarrow$ GTG
• Glutamic acid $\rightarrow$ Valine
• One base change, big impact

Remember: Small mutation, serious disease.

Answer 1

Concept: Mutations are changes in the DNA sequence. A point mutation is the simplest type of mutation involving a single nucleotide change.
Definition: A point mutation is a genetic mutation in which a single nucleotide base is altered, inserted, or deleted in the DNA sequence. Most commonly, it involves substitution of one base for another.
Example: Sickle Cell Anemia Sickle cell anemia is a classic example of a point mutation affecting hemoglobin.
Cause:

• Mutation occurs in the gene encoding the $\beta$-chain of hemoglobin.
• A single base substitution changes the codon.

Molecular Change: \[ \text{Normal codon: GAG} \rightarrow \text{Glutamic acid} \] \[ \text{Mutated codon: GTG} \rightarrow \text{Valine} \] This substitution changes one amino acid in the hemoglobin protein.
Effect:

• Hemoglobin becomes abnormal (HbS).
• RBCs become sickle-shaped under low oxygen conditions.
• Leads to anemia, pain, and reduced oxygen transport.

Significance:

• Demonstrates how a single nucleotide change can cause a major disorder.
• Example of a missense mutation.