Select the incorrect statement from the following

Options

A. Plasmid DNA+COS sites of DNA of `lambda` phage = Cosmid
B. `M_(13)` phage DNA + Ecoli plasmid DNA = Phagemid
C. Cosmid is a modified circular, ds vector DNA
D. Cosmid carry selectively very small foreign DNA fragments into the host cells

Answer

To solve the question of selecting the incorrect statement, we will analyze each of the provided statements one by one.

### Step-by-Step Solution:

1. **Statement 1**: "Plasmid DNA and cos site of the DNA of lambda phage is called as cosmid."
- **Analysis**: This statement is correct. Cosmids are indeed vectors that contain a plasmid origin of replication and a cos site derived from lambda phage.

2. **Statement 2**: "M13 phage DNA and E. coli plasmid have a phagemid."
- **Analysis**: This statement is also correct. A phagemid is a type of vector that combines features of both plasmids and bacteriophages, specifically M13 phage DNA and E. coli plasmid.

3. **Statement 3**: "Cosmid is a modified circular double-stranded vector DNA."
- **Analysis**: This statement is incorrect. Cosmids are not described as modified circular double-stranded vectors; they are already circular and serve as vectors without needing modification.

4. **Statement 4**: "Cosmid carries selectively very small foreign DNA fragments into the host cell."
- **Analysis**: This statement is correct. Cosmids are designed to carry foreign DNA into host cells, and they can accommodate relatively small DNA fragments.

### Conclusion:
The incorrect statement is **Statement 3**: "Cosmid is a modified circular double-stranded vector DNA."

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