Cloning vector: The DNA molecule originating from the virus, a plasmid, or the cell of a higher organism into which an another DNA fragment of appropriate size can be integrated without any loss of the vectors capacity for the self- replication; vectors introduce foreign DNA into the host cells, where it can be reproduced in large quantities. The examples for this are cosmids, plasmids, bacterial artificial chromosomes (BAC) and yeast artificial chromosomes (YAC); vectors are frequently recombinant molecules containing the DNA sequences from several sources.