Vectors constructed by combining certain features of plasmid and the cos sites of phage lambda are called:

Options

A. BACs
B. Phagmids
C. Cosmids
D. Shuttle vectors

Answer

To solve the question regarding the type of vectors constructed by combining certain features of plasmids and the cos sites of phage lambda, we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Components**:
- The question mentions "plasmid" and "cos sites of phage lambda".
- Plasmids are small, circular DNA molecules that can replicate independently of chromosomal DNA in bacteria.
- The cos site is a specific sequence in the lambda phage that is essential for the packaging of the phage DNA into the viral capsid.

2. **Identify the Vector Types**:
- We need to evaluate the options provided: Bacterial Artificial Chromosome (BAC), Phasmid, Cosmid vector, and Shuttle vector.

3. **Evaluate Each Option**:
- **Bacterial Artificial Chromosome (BAC)**: This is a vector used for cloning large DNA fragments, but it is primarily based on plasmid features and does not incorporate cos sites. Thus, this option is incorrect.
- **Phasmid**: This is a vector that combines features of plasmids and bacteriophages, but it does not specifically incorporate the cos sites of lambda phage. Therefore, this option is also incorrect.
- **Cosmid Vector**: A cosmid is indeed a hybrid vector that combines plasmid features with the cos sites of lambda phage. This allows for the cloning of larger DNA fragments than typical plasmids. Hence, this option is correct.
- **Shuttle Vector**: These vectors can replicate in two different host organisms but do not specifically combine plasmid features with cos sites. Thus, this option is incorrect.

4. **Conclusion**:
- After evaluating all options, the correct answer is **Cosmid vector**, as it is the only vector that combines the features of plasmids with the cos sites of phage lambda.

### Final Answer:
The vectors constructed by combining certain features of plasmids and the cos sites of phage lambda are called **Cosmid vectors**.

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