Cloning vector: A DNA molecule originating from a virus, a plasmid (see below) or the cell of a higher organism into which another DNA fragment can be integrated without loss of the vector's (carrier's) capacity for self-replication.

Cloning vectors are used to introduce foreign DNA into host cells, where that DNA can be reproduced (cloned) in large quantities.

Examples of cloning vectors are plasmids, cosmids, and yeast artificial chromosomes (YACs):

• Plasmid: Autonomously (self) replicating, extrachromosomal circular DNA molecules, distinct from the normal bacterial genome and usually not essential for cell survival. Some plasmids are capable of integrating into the host genome. A number of artificially constructed plasmids are used as cloning vectors.
• Cosmid: An artificially constructed cloning vector containing a gene (the cos gene) of the virus called phage lambda. Cosmids can be packaged in lambda phage particles for infection into the bacteria E. coli; this permits the cloning of larger DNA fragments than can be introduced into bacterial hosts using plasmid vectors.
• Yeast artificial chromosomes (YAC): A vector (carrier) created and used in the laboratory to clone pieces of DNA, a YAC is constructed from the telomeric (end), centromeric, and replication origin sequences needed for the replication of the cloned DNA within yeast cells.

Cloning vectors are often recombinant DNA molecules containing DNA sequences from several sources.