Question

Transition mutation is due to replacement of

• A. GC by TA
• B. AT by CG
• C. CG by GC
• D. AT by GC

Answer 1

The correct option is C

Explanation of the correct answer:

• A transition mutation is a point mutation that changes a purine nucleotide to another purine (A ↔ G) or a pyrimidine nucleotide to another pyrimidine (C ↔ T).
• A is a purine and T is a pyrimidine, which are replaced by G and C, respectively, and G is another purine and C is another pyrimidine.

Explanation of the incorrect answers:

Option A:

• In this option A is a purine which is being replaced by pyrimidine C.
• T is a pyrimidine which is being replaced by the purine G.
• Such type of point mutation in DNA in which a single (two ring) purine (A or G) is changed for a (one ring) pyrimidine (T or C), or vice versa, is called transverse mutation.

Option B:

• C is pyrimidine and G is purine.
• Hence, this is also a transverse mutation, not transition mutation.

Option D:

• G purine is replaced by T pyrimidine and C pyrimidine is replaced by A purine.
• This is also a transverse mutation and not transition mutation.

Final answer: Transition mutation is due to replacement of AT by GC.