A single strand of nucleic acid tagged with a radioactive molecule is called:

Options

A. probe
B. vector
C. plasmid
D. selectable marker

Answer

To answer the question "A single strand of nucleic acid tagged with a radioactive molecule is called:", we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Question**: The question is asking for the term used to describe a single strand of nucleic acid that has been tagged with a radioactive molecule.

2. **Analyze the Options**: The options given are:
- Probe
- Vector
- Plasmid
- Selectable Marker

3. **Define Each Term**:
- **Probe**: A probe is a single-stranded nucleic acid (DNA or RNA) that is labeled with a radioactive or fluorescent molecule. It is used to detect specific sequences of nucleic acids in a sample.
- **Vector**: A vector is a DNA molecule used to carry foreign genetic material into another cell. It is not specifically a single strand of nucleic acid tagged with a radioactive molecule.
- **Plasmid**: A plasmid is a small, circular piece of DNA that is separate from chromosomal DNA and can replicate independently. It is not a single strand of nucleic acid tagged with a radioactive molecule.
- **Selectable Marker**: A selectable marker is a gene used to identify cells that have taken up a foreign gene. It does not refer to a single strand of nucleic acid tagged with a radioactive molecule.

4. **Identify the Correct Answer**: Based on the definitions, the correct term for a single strand of nucleic acid tagged with a radioactive molecule is **Probe**.

5. **Conclusion**: Therefore, the answer to the question is that a single strand of nucleic acid tagged with a radioactive molecule is called a **Probe**.