Restriction endonucleases are useful in

Options

A. Breaking DNA at specific sites
B. Creating sticky ends
C. Both A and B
D. Crossing over.

Answer

**Step-by-Step Solution:**

1. **Understanding Restriction Endonucleases:**
- Restriction endonucleases, also known as restriction enzymes, are proteins that cut DNA at specific sequences known as restriction sites.

2. **Function of Restriction Endonucleases:**
- These enzymes recognize specific short sequences of nucleotides in the DNA and cleave the DNA at these sites. This process is crucial for various molecular biology applications.

3. **Formation of Sticky Ends:**
- When restriction endonucleases cut DNA, they can create "sticky ends." These are overhanging sequences of single-stranded DNA that can easily pair with complementary sequences, facilitating the ligation of DNA fragments.

4. **Analyzing the Options:**
- The options provided are:
A. Breaking DNA at specific sites
B. Creating sticky ends
C. Both A and B
D. Crossing over
- From our understanding, both A and B are true statements about the functions of restriction endonucleases.

5. **Eliminating Incorrect Options:**
- Option D, "crossing over," refers to the exchange of genetic material between homologous chromosomes during meiosis, which does not involve restriction endonucleases. Therefore, it is incorrect.

6. **Conclusion:**
- Since both A and B are correct, the answer is option C: "Both A and B."

**Final Answer:**
- The correct answer is **C. Both A and B.**

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