Question

The classical example of point mutation is

• A. Haemophilia
• B. Sickle cell anaemia
• C. Cystic fibrosis
• D. Phenyl ketonuria

Hint:

Sickle cell anaemia = Point Mutation (Transversion from GAG to GUG). Frame-shift mutations are caused by insertions or deletions, not simple single base substitutions.

Answer 1

The Correct Option is B

Step 1: Understanding the Concept: A point mutation is a specific type of genetic mutation where a single nucleotide base is altered (changed, inserted, or deleted) in a DNA or RNA sequence.
Step 2: Key Formula or Approach: Identify which of the given genetic disorders is fundamentally caused by a single base substitution at the molecular level.
Step 3: Detailed Explanation: Sickle cell anaemia is the universally taught classical example of a point mutation.
It is caused by the substitution of a single nitrogenous base in the DNA sequence coding for the $\beta$-globin chain of hemoglobin.
Specifically, an Adenine is replaced by a Thymine (the sequence GAG mutates to GTG in DNA, leading to GAG changing to GUG in the mRNA).
This single base change results in the substitution of the amino acid glutamic acid with valine at the 6th position of the $\beta$-globin chain.
This slight change drastically alters the physical shape of the red blood cell under low oxygen tension, causing it to become sickle-shaped.
Step 4: Final Answer: The correct option is (2).