The experimental system used in studies of the discovery of replication of DNA has been

Options

A. Drosophila melanogaster
B. Pneumococcus
C. Escherichia coli
D. Neurospora crassa

Explanation

**Step-by-Step Solution:**

1. **Identify the Question**: The question asks for the experimental system used in studies of the discovery of DNA replication.

2. **Recall Relevant Information**: The video transcript mentions several organisms, including Drosophila melanogaster, Pneumonococcus, Escherichia coli (E. coli), and Neurospora crassa, but specifically highlights E. coli as the organism used in the studies conducted by Messelson and Stahl.

3. **Understand the Choice of E. coli**: The transcript provides four reasons why E. coli was chosen for DNA replication studies:
- **Rapid Generation Time**: E. coli has a generation time of approximately 20 minutes, allowing for quick results in experiments.
- **Ease of Maintenance**: E. coli is easy to maintain in a laboratory setting and is cost-effective.
- **Wide Range of Survival Conditions**: E. coli can survive in a variety of environmental conditions, including harsh ones.
- **Harmless Environmental Strains**: The strains of E. coli used in research are generally non-pathogenic, reducing the risk of disease during experiments.

4. **Conclude the Answer**: Based on the information provided, the experimental system used in studies of the discovery of DNA replication is **Escherichia coli (E. coli)**.

**Final Answer**: Escherichia coli (E. coli)

---