Thermal cycler is used in the reaction:

Options

A. Radioactivity
B. Chemical reactions
C. Polymerase chain reaction
D. Enzyme catalysed reactions

Answer

### Step-by-Step Solution:

1. **Understanding the Thermal Cycler**: A thermal cycler is an instrument used in molecular biology to amplify DNA and perform various temperature-dependent reactions.

2. **Identifying the Main Function**: The primary function of a thermal cycler is to facilitate the Polymerase Chain Reaction (PCR), which is a technique used to amplify specific DNA segments.

3. **Recognizing PCR Steps**: PCR involves three main steps:
- **Denaturation**: Heating the DNA to around 95°C to separate the strands.
- **Annealing**: Cooling the mixture to about 55°C to allow primers to bind to the target DNA.
- **Extension**: Raising the temperature to approximately 72°C for the DNA polymerase (Taq polymerase) to synthesize new DNA strands.

4. **Conclusion**: Given that the thermal cycler is specifically designed to control the temperature cycles required for PCR, it is clear that the correct answer to the question is "Polymerase Chain Reaction."

### Final Answer:
The thermal cycler is used in the reaction: **Polymerase Chain Reaction (PCR)**.

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