Which of the following is true about RNAi process ?

Options

A. It is a method of cellular defense.
B. It involves silencing of a specific mRNA due to a complementary RNA molecule.
C. The source of complementary RNA in this process may be infection by viruses having RNA genomes.
D. All are true

Answer

To solve the question "Which of the following is true about the RNAi process?", we will analyze each of the provided statements regarding RNA interference (RNAi) and determine their validity step by step.

### Step-by-Step Solution:

1. **Understanding RNAi**:
- RNA interference (RNAi) is a biological process in which RNA molecules inhibit gene expression or translation, by neutralizing targeted mRNA molecules.

2. **Evaluating the First Statement**:
- The first statement claims that RNAi is a method of cellular defense.
- **Analysis**: This is true. RNAi serves as a defense mechanism against viruses and transposons by degrading their RNA, thus preventing the expression of harmful genes.

3. **Evaluating the Second Statement**:
- The second statement mentions that RNAi involves silencing of specific mRNA due to a complementary RNA molecule.
- **Analysis**: This is also true. The process involves small interfering RNAs (siRNAs) or microRNAs (miRNAs) that are complementary to the target mRNA, leading to its degradation or inhibition of translation.

4. **Evaluating the Third Statement**:
- The third statement states that the source of complementary RNA in this process may be infection by viruses having an RNA genome.
- **Analysis**: This is correct as well. Viruses with RNA genomes can introduce RNA into the host cell, which can then be processed into siRNAs that target and silence the viral RNA.

5. **Final Evaluation**:
- Since all three statements are true, the last option, which states "All are true," is the correct answer.

### Conclusion:
- The correct answer to the question is **Option 4: All are true**.