What are true of Plasmids

Options

A. They are found in viruses
B. They are main parts of chromosomes
C. They are widely used in gene transfer
D. They contain gene for vital activities

Answer

### Step-by-Step Solution:

1. **Definition of Plasmids**:
- Plasmids are extra-chromosomal DNA molecules found in cells, primarily in bacteria. They exist independently of the chromosomal DNA and are typically circular in shape.

2. **Function of Plasmids**:
- Unlike chromosomal DNA, which contains essential genes necessary for the basic functions of the cell, plasmids often carry genes that can provide additional advantages, such as antibiotic resistance or other traits that may benefit the organism under certain conditions.

3. **Location of Plasmids**:
- Plasmids are not found in viruses; they are predominantly found in bacteria. This eliminates options that suggest plasmids are a main part of the chromosome or that they are found in viruses.

4. **Role in Gene Transfer**:
- Plasmids are widely used in biotechnology for gene transfer. Scientists can insert desired DNA sequences into plasmids, which can then be introduced into host cells, facilitating the transfer of genes.

5. **Vital Activities**:
- Plasmids do not contain genes necessary for vital activities; these are primarily encoded in the chromosomal DNA. Thus, any statement suggesting that plasmids are essential for vital functions is incorrect.

6. **Conclusion**:
- The only true statement about plasmids is that they are widely used in gene transfer.