Question

Identify the vector suitable for cloning long DNA fragments.

• A. Phage vector
• B. Bacterial plasmid
• C. Yeast plasmid
• D. Cosmids

Answer 1

The correct option is D Cosmids

Vector
Vectors are the DNA molecules which can carry the foreign DNA fragment into the host cells for cloning. Examples include the following:

• Plasmids
• Phage vectors
• Yeast plasmids
• Cosmids

Phage vector
Phage vectors have a phage genome into which the DNA of interest encoding the protein is inserted. For example, the lambda phage vector can carry DNA inserts of about
$35-45kbp$.

Plasmids
Plasmids are circular, extranuclear, double stranded, self replicating DNA molecules that are used as vectors for small fragments of DNA. Usually most plasmids carry DNA inserts of about $15kbp$ in size.

Yeast plasmids
Yeast plasmids contain self replicating sequences derived from the yeast chromosome. They are used to clone eukaryotic DNA and up to $40kbp$ can be inserted into these plasmids.

Cosmids
Cosmids are hybrid plasmids containing a bacterial ori site and a ‘cos’ sequence from lambda phage. The ‘cos’ sites help the cosmid in its packaging into the capsids of viral particles. The cosmids are used to carry large DNA molecules of $40-50kbp$.

Final answer:
d. Cosmids