A number of plant and animal viruses have also been used as vectors both for introducing foreign genes into cells and for gene amplification and expression in the host cells. Bacteriophages are viruses that attack bacteria. Most phages lyse the bacterial cells they infect (lytic phages). But many others can chose to follow either a lytic or a lysogenic cycle; in the latter situation, the phage chromosome integrates into the bacterial chromosome and multiplies with the latter as prophage (temperate or lysogenic phages). The prophage may dissociate from the bacterial chromosome and follows the lytic cycle.
Cauliflower mosaic virus, tobacco mosaic virus and geminiviruses are three groups of viruses that have been used as vectors for cloning of DNA segments.