Viruses: Viruses are natural vectors that can transfer DNA between different organisms. Some viruses, such as bacteriophages, can infect bacteria and insert their own DNA into the bacterial genome. Other viruses, such as retroviruses, can insert their DNA into the genome of eukaryotic cells.
Plasmids: Plasmids are small, circular DNA molecules that can replicate independently of chromosomal DNA. Plasmids can be engineered to carry foreign DNA and can be transferred between bacteria through a process called conjugation.
Cosmids: Cosmids are large plasmids that can carry larger DNA fragments than plasmids. Cosmids can be used to clone DNA fragments up to 40 kilobases in size.
Bacterial artificial chromosomes (BACs): BACs are large, circular DNA molecules that can carry DNA fragments up to 300 kilobases in size. BACs are used to clone large DNA fragments that cannot be cloned in plasmids or cosmids.
Yeast artificial chromosomes (YACs): YACs are large, circular DNA molecules that can carry DNA fragments up to 1 megabase in size. YACs are used to clone very large DNA fragments that cannot be cloned in BACs.
