Which class of restriction endonucleases is/are not used in recombinant DNA technology?

Options

A. Type I
B. Type II
C. Type III
D. Type I and III

Answer

To answer the question regarding which class of restriction endonucleases is/are not used in recombinant DNA technology, we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Types of Restriction Endonucleases**:
- There are three main types of restriction endonucleases: Type I, Type II, and Type III. Each type has different mechanisms and functions.

2. **Analyze Type I Restriction Endonucleases**:
- Type I restriction enzymes have a single enzyme that performs both restriction and methylation. However, their restriction activity occurs randomly and not at the specific recognition site. This randomness makes them less useful for precise genetic engineering.

3. **Analyze Type II Restriction Endonucleases**:
- Type II restriction enzymes are the most commonly used in recombinant DNA technology. They have specific recognition sites and cut DNA at these sites. This specificity is crucial for genetic engineering applications.

4. **Analyze Type III Restriction Endonucleases**:
- Type III restriction enzymes also have separate enzymes for restriction and methylation. They cleave DNA outside of the recognition site, which again makes them less suitable for precise applications in recombinant DNA technology.

5. **Conclusion**:
- Based on the analysis, both Type I and Type III restriction endonucleases are not used in recombinant DNA technology due to their random cutting and lack of specificity. Therefore, the correct answer is that Type I and Type III restriction endonucleases are not used in recombinant DNA technology.

### Final Answer:
The classes of restriction endonucleases that are not used in recombinant DNA technology are Type I and Type III.

---