Sickle cell anemia is an example of which type of mutation?

The correct answer is Option (3) → Point mutation

A mutation is a change in the genetic material. When the change affects only one base pair of DNA, it is called a point mutation. In sickle-cell anaemia, one base of the beta globin gene is replaced (GAG becomes GUG at the sixth codon), so glutamic acid is replaced by valine in the beta chain of haemoglobin.

Option (1) Insertion — Incorrect. An insertion adds base pairs to DNA. Insertions and deletions cause frame-shift mutations, which change the reading of every codon after the change. In sickle-cell anaemia no base is added.

Option (2) Deletion — Incorrect. A deletion removes base pairs and also causes a frame-shift. In sickle-cell anaemia no base is lost; one base is replaced by another.

Option (3) Point mutation — Correct. Sickle-cell anaemia is the classical example of a point mutation: a single base substitution in the gene for the beta chain of haemoglobin.

NCERT Extract:
Mutation – “… In addition to the above, mutation also arise due to change in a single base pair of DNA. This is known as point mutation. A classical example of such a mutation is sickle cell anemia. Deletions and insertions of base pairs of DNA, causes frame-shift mutations (see Chapter 5).”
Mendelian Disorders – “… The substitution of amino acid in the globin protein results due to the single base substitution at the sixth codon of the beta globin gene from GAG to GUG. The mutant haemoglobin molecule undergoes polymerisation under low oxygen tension causing the change in the shape of the RBC from biconcave disc to elongated sickle like structure ….”