Find the true statement from the following

Options

A. Ori means origin of transcription.
B. Some bacterial cell may have copy number of plasmid that varies from 15 - 100.
C. Vector should have many recognition sites for commonly used restriction enzymes so that alien DNA can attach to any one of the sites easily.
D. An ideal vector should have ori, site restriction site for different REN but not a selectable marker.

Answer

To solve the question "Find the true statement from the following," we will analyze each option provided and determine which statement is correct.

### Step-by-Step Solution:

1. **Analyze the First Statement:**
- **Statement:** "ori means origin of transcription."
- **Analysis:** The term "ori" actually stands for "origin of replication," not transcription. Therefore, this statement is **incorrect**.

2. **Analyze the Second Statement:**
- **Statement:** "Some bacterial cells may have a copy number of plasmid that varies from 15 to 100."
- **Analysis:** This statement is true. Bacterial cells can have varying numbers of plasmids, ranging from 1 to 2 copies to as many as 15 to 100 copies per cell. Thus, this statement is **correct**.

3. **Analyze the Third Statement:**
- **Statement:** "Vector should have many recognizable sites for commonly used restriction enzymes so that alien DNA can attach to any one of the sites easily."
- **Analysis:** While having multiple restriction sites is beneficial, it is not necessary for a vector to have many sites; it can function with fewer sites as well. Therefore, this statement is **incorrect**.

4. **Analyze the Fourth Statement:**
- **Statement:** "An ideal vector should have an ori site, restriction site for different alien DNA, but not a selectable marker."
- **Analysis:** This statement is incorrect because a selectable marker is essential for identifying or eliminating non-transformants. An ideal vector should indeed include a selectable marker. Thus, this statement is **incorrect**.

### Conclusion:
After analyzing all the statements, the only true statement is the **second statement**: "Some bacterial cells may have a copy number of plasmid that varies from 15 to 100."

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