A method in which recombinant DNAs are incubated with host cells on ice, followed by placing them briefly at `42^(@)`C and then putting them back on ice is called:

Options

A. Heat shock method
B. Transfection
C. Biolistics
D. Gene gun

Answer

**Step-by-Step Solution:**

1. **Understanding the Question**: The question asks for a specific method of introducing recombinant DNA into host cells that involves a sequence of temperature changes: incubation on ice, a brief exposure to 42°C, and then returning to ice.

2. **Identifying the Options**: The options provided are:
- Heat shock method
- Transfection
- Biolistics
- Gene gun

3. **Analyzing Each Option**:
- **Heat Shock Method**: This method involves incubating cells with recombinant DNA on ice, followed by a rapid increase in temperature (to around 42°C) and then returning to ice. This process creates pores in the cell membrane, allowing the DNA to enter the cells.
- **Transfection**: This is a broader term that refers to the introduction of nucleic acids into cells but does not specifically describe the temperature cycling mentioned in the question.
- **Biolistics/Gene Gun**: This method involves physically delivering DNA into cells using high-velocity microprojectiles. It does not involve temperature changes as described in the question.

4. **Conclusion**: Based on the analysis, the method that matches the description given in the question is the **Heat Shock Method**.

5. **Final Answer**: The correct answer is **Heat Shock Method**.

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