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

Options

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

Explanation

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 Types of Mutations**:
- Familiarize yourself with the different types of mutations: frameshift mutation, transition, transversion, and transcription.

2. **Define Frameshift Mutation**:
- A frameshift mutation occurs when nucleotides are inserted or deleted from the DNA sequence, which alters the reading frame of the genetic code. This is not applicable in our case since we are only replacing one base with another.

3. **Define Transcription**:
- Transcription is the process where DNA is converted into RNA. This is not a type of mutation, so it does not apply here.

4. **Define Transition Mutation**:
- A transition mutation is a specific type of point mutation where a purine is replaced by another purine (adenine ↔ guanine) or a pyrimidine is replaced by another pyrimidine (cytosine ↔ thymine). In our case, adenine (a purine) is replaced by guanine (another purine), which fits this definition.

5. **Define Transversion Mutation**:
- A transversion mutation is when a purine is replaced by a pyrimidine or vice versa. Since we are dealing with two purines (adenine and guanine), this option is not applicable.

6. **Conclusion**:
- Since adenine is replaced by guanine, which are both purines, this event is classified as a transition mutation.

### Final Answer:
The correct answer is **transition**.