DNA or RNA segment tagged with a radiactive molecule is called

Options

A. Clone
B. Plasmid
C. Vector
D. Probe

Answer

To answer the question, "DNA or RNA segment tagged with a radioactive molecule is called," we can follow these steps:

### Step-by-Step Solution:

1. **Understanding the Terms**:
- First, we need to understand the terms mentioned in the options: clone, plasmid, vector, and probe.

2. **Defining Clone**:
- A clone refers to an identical copy of a parent organism or DNA. It does not relate to the tagging of DNA or RNA with radioactive molecules. Therefore, this option is incorrect.

3. **Defining Plasmid**:
- A plasmid is a small, circular piece of DNA that is separate from chromosomal DNA and can replicate independently. It is often used as a vector in genetic engineering but does not refer to a tagged segment. Thus, this option is also incorrect.

4. **Defining Vector**:
- A vector is a vehicle used to transfer genetic material into a cell. While vectors can carry genes, they do not specifically refer to segments tagged with radioactive molecules. Therefore, this option is incorrect as well.

5. **Defining Probe**:
- A probe is a segment of DNA or RNA that is labeled or tagged with a radioactive molecule. Probes are used in various molecular biology techniques to detect specific sequences of nucleic acids. This matches the description given in the question.

6. **Conclusion**:
- Based on the definitions and analysis, the correct answer to the question is that a DNA or RNA segment tagged with a radioactive molecule is called a **probe**.

### Final Answer:
A DNA or RNA segment tagged with a radioactive molecule is called a **probe**.