There are several types of vector DNA for molecular cloning .
Plasmids are extrachromosomal DNA elements.
Plasmids are used widely in cloning in bacteria. These are all designed as shuttle plasmids, capable of replicating as plasmids in E. coli and in yeast. The E. coli lambda phage contains 40 kbp of double-stranded DNA and can be used to carry DNA fragments up to about 20kbp. Cosmids are plasmids that contain part of lambda phage DNA, allowing the packaging of the DNA into lambda phage particles. The P1 bacteriophage can accomodate more DNA than lambda and is the basis for PAC vectors .