One gene - one enzyme relationship was established for the first time on

Options

A. salmonella typhimurium
B. Escherichia coli
C. Diplococcus pneumoniae
D. Neurospora crassa

Answer

**Step-by-Step Solution:**

1. **Understanding the Question**: The question asks about the organism on which the "one gene - one enzyme" relationship was first established.

2. **Identifying Key Scientists**: The "one gene - one enzyme" hypothesis was proposed by scientists George Beadle and Edward Tatum.

3. **Historical Context**: This hypothesis was established in 1941, and Beadle and Tatum were awarded the Nobel Prize in 1958 for their work.

4. **Experimental Organism**: The experiments that led to the establishment of this hypothesis were conducted using the organism Neurospora crassa, which is a type of red mold.

5. **Significance of the Experiment**: Beadle and Tatum irradiated Neurospora crassa with X-rays, which resulted in mutations that made the mold unable to synthesize certain amino acids. This led to the conclusion that each gene is responsible for the production of a specific enzyme.

6. **Evaluating the Options**:
- Salmonella Typhimurium: Incorrect
- Escherichia coli: Incorrect
- Diplococcus pneumoniae: Incorrect
- Neurospora crassa: Correct

7. **Conclusion**: Therefore, the correct answer to the question is Neurospora crassa.

**Final Answer**: Neurospora crassa

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