Which of the following has popularised the PCR (polymerase chain reactions)?

Options

A. Easy availability of DNA template
B. Availability of synthetic primers
C. Availability of cheap deoxyribonucleotides
D. Availability of 'Thermostable' DNA polymerase

Answer

To solve the question "Which of the following has popularised the PCR (polymerase chain reactions)?", we need to analyze the options provided and understand the significance of each in the context of PCR.

### Step-by-Step Solution:

1. **Understanding PCR**:
- PCR, or Polymerase Chain Reaction, is a technique used to amplify specific DNA segments, creating millions of copies of a particular DNA sequence in vitro (outside of a living organism).

2. **Analyzing the Options**:
- **Option 1: Easy availability of DNA template**: While having a DNA template is necessary for PCR, it does not specifically contribute to the popularity of the technique itself.
- **Option 2: Availability of synthetic primers**: Synthetic primers are essential for initiating the PCR process, but their availability alone does not make PCR popular.
- **Option 3: Availability of 3-deoxyribonucleotide**: This option is not directly relevant to the PCR process, as PCR primarily uses deoxyribonucleotides (dNTPs) rather than 3-deoxyribonucleotides.
- **Option 4: Availability of thermo-stable DNA polymerase**: This is a crucial factor. The enzyme used in PCR, known as Taq polymerase, is derived from the thermophilic bacterium Thermus aquaticus. This enzyme can withstand the high temperatures required for the denaturation step of PCR, making it essential for the process.

3. **Conclusion**:
- The factor that has most significantly popularized PCR is the availability of thermo-stable DNA polymerase. This allows the PCR process to be conducted efficiently at high temperatures, which is critical for the denaturation of DNA strands.

### Final Answer:
**Option 4: Availability of thermo-stable DNA polymerase.**

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