In the nomenclature of enzyme restriction endonuclease the Roman numerical indicates

Options

A. (a) Number of times it is used
B. (b) The order of discovery from source
C. (c) Number of cuts on DNA
D. (d) Number of recombinants formed

Answer

**Step-by-Step Solution:**

1. **Understanding the Nomenclature**: The nomenclature of restriction endonucleases typically consists of three parts: a letter indicating the genus, a letter indicating the species, and a letter indicating the strain, followed by a Roman numeral.

2. **Example Breakdown**: Take the example of EcoR1:
- **E** stands for the genus "Escherichia".
- **Co** stands for the species "coli".
- **R** represents the strain, which in this case is "R by 13".

3. **Identifying the Roman Numeral**: The Roman numeral in the name (in this case, "1") indicates the order of discovery of that particular restriction endonuclease from the bacterial strain.

4. **Conclusion**: Therefore, in the nomenclature of enzyme restriction endonucleases, the Roman numeral indicates the order of discovery from the source, which is the bacteria.

5. **Final Answer**: The correct answer is option B: "the order of discovery from the source".

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