Vectors are tools used by molecular biologists to insert genes or pieces of foreign DNA into host cells. The four main types of vector commonly used include plasmids, bacteriophages, cosmids and yeast artificial chromosomes (YAC’s).
Plasmid: It is an extra chromosomal circular DNA molecule that independently replicates inside the bacterial cell and some yeasts; cloning limit: 100 to 10,000 base pairs or 0.1-10 kilobases (kb).
Phage : Designed bacteriophage lambda (λ) and M13 ; linear DNA molecules, whose region can be replaced with foreign DNA without disrupting its life cycle; cloning limit: 8-20 kb. M13 is a filamentous phage which infects E-coli. cloning limit: 10 kb.
Cosmids: A constructed extrachromosomal circular DNA molecule that combines features of plasmids and (cos) sites of phage; cloning limit: 45 kb.
Yeast Artificial Chromosomes (YAC): An artificial chromosome that contains telomeres, origin of replication, a yeast centromere, restriction enzymes sites and a selectable marker for identification in yeast cells ; cloning limit: 1Mb.
