In rDNA technology, the term 'vector' refers to

Options

A. the enzyme that cuts DNA fragment
B. the sticky end of a DNA fragment.
C. a plasmid used to transfer DNA into a living cell.
D. a DNA probe used to identify a particular gene

Answer

To solve the question regarding the term 'vector' in rDNA technology, we will analyze each option provided and determine which one correctly defines a vector in this context.

### Step-by-Step Solution:

1. **Understanding the Question**: The question asks for the definition of 'vector' in the context of recombinant DNA (rDNA) technology.

2. **Analyzing the Options**:
- **Option A**: The enzyme that cuts DNA fragment.
- This refers to restriction enzymes, which are not vectors but tools used in rDNA technology.
- **Option B**: The sticky end of a DNA fragment.
- Sticky ends are the overhanging ends of DNA fragments that can anneal to complementary sequences, but they do not define a vector.
- **Option C**: A plasmid used to transfer DNA into a living cell.
- This is a correct definition. Plasmids are circular DNA molecules that can carry foreign DNA and facilitate its transfer into host cells.
- **Option D**: A DNA probe used to identify a particular gene.
- DNA probes are used for detection and identification of specific sequences, but they are not vectors.

3. **Selecting the Correct Option**: Based on the analysis, Option C is the only one that accurately describes a vector in rDNA technology. Vectors are indeed DNA molecules (like plasmids) that are used to transfer foreign DNA into living cells where it can replicate.

### Conclusion:
The correct answer is **Option C: a plasmid used to transfer DNA into a living cell**.

---