Extrachromosomal DNA used as vector in gene cloning is

Options

A. Transposon
B. Intron
C. Exon
D. Plasmid

Answer

**Step-by-Step Solution:**

1. **Understanding Extrachromosomal DNA**:
- Extrachromosomal DNA refers to DNA that is not part of the chromosomal DNA found in the nucleus. In prokaryotes, such as bacteria, this DNA exists outside of the main chromosomal DNA.

2. **Identifying Types of Extrachromosomal DNA**:
- In bacteria, extrachromosomal DNA can take the form of plasmids. Plasmids are small, circular DNA molecules that can replicate independently of the chromosomal DNA.

3. **Functions of Plasmids**:
- Plasmids can carry genes that provide bacteria with advantageous traits, such as antibiotic resistance (R-plasmids) or the ability to conjugate with other bacteria (fertility plasmids).

4. **Analyzing the Options**:
- The question provides multiple options regarding the type of extrachromosomal DNA used as vectors in gene cloning.
- The correct option is the one that refers specifically to plasmids, as they are commonly used in genetic engineering for cloning purposes.

5. **Conclusion**:
- The correct answer to the question is that the extrachromosomal DNA used as a vector in gene cloning is **plasmids**.

**Final Answer**: Plasmids (Option 4).

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