Which of the following phenomena was experimentally proved by Meselson and Stahl?

Options

A. Transformation
B. Transduction
C. Semi-conservative DNA replication
D. Central dogma

Explanation

**Step-by-Step Solution:**

1. **Understanding the Question**: The question asks which phenomenon was experimentally demonstrated by Meselson and Stahl. We need to identify the specific aspect of molecular biology they researched.

2. **Identifying the Experiment**: Meselson and Stahl conducted a significant experiment in 1958 to investigate the mechanism of DNA replication. They specifically aimed to determine whether DNA replication is conservative, semi-conservative, or dispersive.

3. **Understanding Semi-Conservative Replication**: In semi-conservative replication, each strand of the original double-stranded DNA serves as a template for the new strand. After replication, each new double helix consists of one old (parental) strand and one newly synthesized strand.

4. **Experimental Method**: Meselson and Stahl used isotopes of nitrogen (N-15 and N-14) to label the DNA in E. coli. By centrifuging the DNA, they were able to observe the density of the DNA strands after several rounds of replication.

5. **Results of the Experiment**: Their results showed that after one round of replication, the DNA had an intermediate density, and after two rounds, there were both light and intermediate density bands. This supported the semi-conservative model of DNA replication.

6. **Conclusion**: Based on their findings, Meselson and Stahl proved that DNA replication is semi-conservative. Therefore, the correct answer to the question is that they experimentally proved semi-conservative DNA replication.

**Final Answer**: Semi-conservative DNA replication.

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