Which of the following organisms was used to establish the semi-conservative nature of DNA?

Options

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

Answer

To determine which organism was used to establish the semi-conservative nature of DNA, we can follow these steps:

### Step 1: Understand the Concept of Semi-Conservative DNA Replication
- Semi-conservative replication means that during DNA replication, each new DNA molecule consists of one old (parent) strand and one newly synthesized strand. This was a key finding in molecular biology.

### Step 2: Identify the Key Experiment
- The semi-conservative nature of DNA replication was established through a famous experiment conducted by scientists Matthew Meselson and Franklin Stahl.

### Step 3: Recognize the Organism Used in the Experiment
- Meselson and Stahl conducted their experiment using the bacterium **Escherichia coli (E. coli)**. They grew E. coli in a medium containing heavy nitrogen (N-15) and then transferred it to a medium with lighter nitrogen (N-14) to observe the DNA replication process.

### Step 4: Analyze the Options Given
- The options provided are:
a. Escherichia coli
b. Neurospora crassa
c. Pneumococcus
d. Drosophila melanogaster
- Based on the experiment by Meselson and Stahl, the correct answer is **a. Escherichia coli**.

### Conclusion
- Therefore, the organism used to establish the semi-conservative nature of DNA is **Escherichia coli**.

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