Transition mutation is due to replacement of

Options

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

Answer

### Step-by-Step Solution:

1. **Understanding Transition Mutation**: Transition mutations involve the substitution of one base for another of the same type. There are two types of nitrogenous bases: purines (adenine and guanine) and pyrimidines (cytosine and thymine). A transition mutation occurs when a purine is replaced by another purine or a pyrimidine is replaced by another pyrimidine.

2. **Analyzing the Options**:
- **Option A (GC by TA)**: This option suggests replacing a purine-pyrimidine pair (G-C) with another purine-pyrimidine pair (T-A). This is not a transition mutation, as it involves different types of bases.
- **Option B (AT by GC)**: This option suggests replacing a purine-pyrimidine pair (A-T) with another purine-pyrimidine pair (G-C). This is also not a transition mutation, as it involves different types of bases.
- **Option C (CG by GC)**: This option suggests replacing a purine-pyrimidine pair (C-G) with another purine-pyrimidine pair (G-C). This is not a transition mutation either.
- **Option D (AT by GC)**: This option suggests replacing a purine-pyrimidine pair (A-T) with another purine-pyrimidine pair (G-C). This is also not a transition mutation.

3. **Identifying the Correct Answer**: After analyzing all options, none of them correctly represent a transition mutation. However, if we are to focus on the concept of transition mutations, we would expect to see options like A to G or C to T. Therefore, the question might have been misinterpreted or the options provided do not correctly reflect the definition of transition mutations.

4. **Conclusion**: Based on the definitions and the analysis of the options, it seems that the correct answer should involve the replacement of one purine with another purine or one pyrimidine with another pyrimidine. However, since none of the options correctly describe a transition mutation, we conclude that there may be an error in the question or options provided.