In a mutational event ,when adenine is replaced by guanine , it is a case of?

Options

A. transition
B. transversion
C. transcription
D. frameshift mutation

Answer

To solve the question regarding the mutational event where adenine is replaced by guanine, we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Nucleotides**:
- The four nucleotides in DNA are adenine (A), guanine (G), thymine (T), and cytosine (C).
- Adenine and guanine are classified as purines, while thymine and cytosine are classified as pyrimidines.

2. **Identify the Types of Mutations**:
- There are different types of mutations, including transitions, transversions, transcription, and frameshift mutations.
- A transition mutation occurs when a purine is replaced by another purine (A ↔ G) or a pyrimidine is replaced by another pyrimidine (T ↔ C).
- A transversion mutation occurs when a purine is replaced by a pyrimidine or vice versa (A ↔ T or A ↔ C, G ↔ T or G ↔ C).

3. **Analyze the Given Mutation**:
- In this case, adenine (A) is replaced by guanine (G).
- Since both adenine and guanine are purines, this replacement falls under the category of a transition mutation.

4. **Conclusion**:
- Therefore, the answer to the question is that the mutational event where adenine is replaced by guanine is a case of a **transition mutation**.

### Final Answer:
The mutational event when adenine is replaced by guanine is a case of **transition mutation**.

---