Which of the following is a genetic vector?

Options

A. plasmid
B. phage `lamda`
C. cosmid
D. all of these

Answer

To determine which of the following is a genetic vector, we need to analyze each option provided:

1. **Understanding Genetic Vectors**: Genetic vectors are tools used to introduce foreign DNA into a host organism's cells. They can carry and replicate the DNA of interest.

2. **Evaluating the Options**:
- **Option 1: Plasmid**: Plasmids are small, circular DNA molecules that can replicate independently of chromosomal DNA. They are commonly used in genetic engineering to transfer DNA into bacteria. They can typically carry up to 15 kilobases (KB) of foreign DNA.
- **Option 2: Phage Lambda**: Lambda phage is a type of virus that infects bacteria. It can be used as a vector to introduce foreign DNA into bacterial cells, with a capacity of about 25 KB of foreign DNA.
- **Option 3: Cosmid**: Cosmids are hybrid vectors that combine features of plasmids and phages. They can carry larger fragments of DNA, up to 42 KB, making them useful for cloning larger genes or genomic DNA.
- **Option 4: All of these**: Since all the above options (Plasmid, Phage Lambda, and Cosmid) can serve as genetic vectors, this option suggests that all listed items are genetic vectors.

3. **Conclusion**: Since all three options are indeed genetic vectors, the correct answer is **Option 4: All of these**.

### Step-by-Step Solution:
1. **Identify what a genetic vector is**: A tool for inserting foreign DNA into host cells.
2. **Analyze each option**:
- **Plasmid**: Can carry 15 KB of DNA.
- **Phage Lambda**: Can carry 25 KB of DNA.
- **Cosmid**: Can carry 42 KB of DNA.
3. **Determine if all options are genetic vectors**: All three can introduce foreign DNA into host cells.
4. **Select the correct answer**: Since all options are genetic vectors, the answer is **Option 4: All of these**.