One of the key factors, which makes the plasmid the vector in genetic engineering is

Options

A. its resistance to antibiotics
B. its resistance to restriction enzymes
C. its ability to carry a foreign gene
D. its ability to cause infection in the host

Explanation

To answer the question regarding the key factor that makes plasmids vectors in genetic engineering, we can break down the reasoning as follows:

### Step-by-Step Solution:

1. **Understanding Plasmids**:
- Plasmids are small, circular, double-stranded DNA molecules found in bacteria. They exist independently of chromosomal DNA and are classified as extra-chromosomal DNA.

2. **Self-Replication**:
- One of the most important characteristics of plasmids is their ability to self-replicate. This means they can duplicate themselves independently of the bacterial chromosome, allowing them to be passed on to daughter cells during cell division.

3. **Carrying Foreign Genes**:
- Plasmids can be engineered to carry foreign genes. This ability to incorporate and express foreign DNA is a crucial feature that allows them to be used as vectors in genetic engineering.

4. **Antibiotic Resistance**:
- Many plasmids contain genes that confer antibiotic resistance. This property is significant because it allows researchers to select for cells that have successfully taken up the plasmid (and thus the foreign gene) by growing them in the presence of antibiotics.

5. **Identifying the Key Factor**:
- Among the options provided:
- **Resistance to antibiotics**: While important, it is not the primary reason plasmids are used as vectors.
- **Resistance to restriction enzymes**: This is not a characteristic of plasmids.
- **Ability to carry a foreign gene**: This is indeed a defining feature of vectors.
- **Ability to cause infection in the host**: This is not applicable to plasmids.

6. **Conclusion**:
- The key factor that makes plasmids effective vectors in genetic engineering is their **ability to carry a foreign gene**. This characteristic allows them to be utilized in various genetic engineering applications.

### Final Answer:
The key factor that makes plasmids the vector in genetic engineering is **their ability to carry a foreign gene**.

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