On cooling the two separated strands of DNA again recoil. It is called

Options

A. chain reaction
B. annealing
C. both 1 and 2
D. palindrome

Answer

To solve the question regarding the process that occurs when two separated strands of DNA recoil upon cooling, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding DNA Structure**: DNA consists of two strands that form a double helix. These strands are held together by hydrogen bonds between complementary bases.

2. **Denaturation Process**: When DNA is heated, the hydrogen bonds between the strands break, causing the two strands to separate. This process is known as denaturation.

3. **Cooling the DNA**: After the denaturation step, if the temperature is lowered, the separated strands of DNA can come back together.

4. **Recoil of DNA Strands**: The process where the separated strands of DNA rejoin or "recoil" upon cooling is a crucial step in various molecular biology techniques, including the Polymerase Chain Reaction (PCR).

5. **Identifying the Correct Term**: The specific term used to describe the rejoining of the separated DNA strands upon cooling is called "annealing." During this phase, the complementary bases of the DNA strands align and form hydrogen bonds again.

6. **Conclusion**: Therefore, the correct answer to the question is option B: annealing.

### Final Answer:
The process of cooling the two separated strands of DNA so that they recoil is called **annealing** (Option B).

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