A: Pst I generates single stranded over hanging stretches in DNA after digestion that facilitate ligation.
R: These short extensions can form phosphodiester bonds with their complementary counterparts.

Options

A. If both Assertion & Reason are true and the reason is the correct explanation of the assertion
B. If both Assertion & Reason are true but the reason is not the correct explanation of the assertion
C. If Assertion is true statement but Reason is false
D. If both Assertion and Reason are false statements

Answer

To solve the question regarding the assertion and reason statements about Pst I and its role in DNA ligation, we can break it down into the following steps:

### Step-by-Step Solution:

1. **Understanding the Assertion**:
- The assertion states that Pst I generates single-stranded overhanging stretches in DNA after digestion that facilitate ligation.
- Pst I is a restriction enzyme that cuts DNA at specific palindromic sequences, resulting in the formation of sticky ends (single-stranded overhangs).

2. **Evaluating the Assertion**:
- This statement is true. Pst I cuts the DNA in such a way that it leaves behind unpaired bases, creating sticky ends. These sticky ends are essential for the ligation process, as they allow for the joining of DNA fragments.

3. **Understanding the Reason**:
- The reason states that these short extensions can form phosphodiester bonds with their complementary counterparts.
- Phosphodiester bonds are the covalent bonds that link nucleotides together in a DNA strand, whereas the sticky ends primarily interact through hydrogen bonds.

4. **Evaluating the Reason**:
- This statement is false. The sticky ends formed by Pst I can indeed form hydrogen bonds with complementary bases on another DNA strand, but they do not directly form phosphodiester bonds. Phosphodiester bonds are formed during the ligation process by the enzyme DNA ligase, which connects the sugar-phosphate backbone of the DNA strands.

5. **Conclusion**:
- The assertion is true, while the reason is false. Therefore, the correct answer is that the assertion is true, and the reason is false.

### Final Answer:
- Assertion (A) is true, and Reason (R) is false.

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