Question

In gene mutation, adenine is replaced by guanine. It is

• A. Frame-shift mutation
• B. Transcription
• C. Transition
• D. Transversion

Answer 1

The correct option is C Transition

The transition is the substitution of one type of base by another base of its own type. Hence, purine is replaced with purine (adenine to guanine and vice versa) and pyrimidine is replaced with the pyrimidine (cytosine to thymine/uracil and vice versa) only. In question adenine (purine) is replaced with guanine (purine); it is the transition, option C is correct. Substitution of purine base for a pyrimidine base or substitution of pyrimidine base for a purine base is called as transversion. Hence, adenine is replaced with thymine/ uracil and guanine with cytosine which makes option D incorrect. The gene mutations that alter the base sequence of a whole genetic frame from the point of the mutation are called frame shift mutations. Here, the reading frame of the base sequence is shifted forward (due to insertion of one or more nucleotide base) or in the backward direction (due to deletion of one or more nucleotide base). But the question is about substitution, not about addition or deletion; option A is incorrect. Transcription is the process of RNA synthesis using DNA template strand; it is not a type of change in gene structure, option B is incorrect.