The unequivocal proof of DNA as the genetic material came from the studies on `:`

Options

A. Bacterium
B. Fungus
C. Viroid
D. Bacterial virus

Explanation

**Step-by-Step Solution:**

1. **Understanding the Question**: The question asks for the source of unequivocal proof that DNA is the genetic material. This refers to a specific experiment or study that clearly demonstrated this fact.

2. **Identifying Key Scientists**: The key scientists associated with this proof are Alfred Hershey and Martha Chase. They conducted a pivotal experiment in 1952 that provided strong evidence for DNA being the genetic material.

3. **Experimental Setup**: Hershey and Chase used a type of virus that infects bacteria, known as a bacteriophage (specifically T2 phage). They labeled the DNA and protein components of the bacteriophage with different radioactive isotopes to trace which part entered the bacterial cells.

4. **Labeling the Components**:
- They labeled the DNA with radioactive phosphorus-32 (P-32) because DNA contains phosphorus in its backbone.
- They labeled the protein coat with radioactive sulfur-35 (S-35) because proteins contain sulfur in certain amino acids.

5. **Infection of Bacteria**: The labeled bacteriophages were allowed to infect Escherichia coli (E. coli) bacteria. After infection, the mixture was blended to separate the phage coats from the bacterial cells.

6. **Centrifugation**: The mixture was then centrifuged. The heavier bacterial cells formed a pellet at the bottom, while the lighter phage coats remained in the supernatant.

7. **Analysis of Results**: After centrifugation, Hershey and Chase analyzed the pellet (bacterial cells) and the supernatant (phage coats):
- They found that the radioactive phosphorus (P-32) was present in the bacterial cells, indicating that DNA had entered the cells.
- In contrast, the radioactive sulfur (S-35) was found only in the supernatant, indicating that the protein coat did not enter the bacterial cells.

8. **Conclusion**: The results of the experiment showed that DNA, not protein, is the genetic material that is transferred from the bacteriophage to the bacteria. This provided unequivocal proof that DNA is the genetic material.

9. **Final Answer**: The unequivocal proof of DNA as the genetic material came from the studies on the bacterium, specifically through the experiments conducted by Hershey and Chase using bacteriophages.

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