Inbiologyacloneis a group of individual cells or organisms descended from one progenitor. This means that the members of a clone are genetically identical, because cell replication produces identical daughter cells each time. The use of the wordclonehas been extended to recombinant DNA technology, which has provided scientists with the ability to produce many copies of a single fragment of DNA, such as a gene, creating identical copies thatconstitutea DNA clone. In practice the procedure is carried out by inserting a DNA fragment into a small DNA molecule and then allowing this molecule to replicate inside a simple living cell such as a bacterium. The small replicating molecule is called a DNAvector (carrier). The most commonly used vectors areplasmids (circular DNA molecules that originated frombacteria),viruses, andyeastcells. Plasmids are not a part of the main cellular genome, but they can carry genes that provide the host cell with useful properties, such asdrug resistance, mating ability, and toxin production. They are small enough to be conveniently manipulated experimentally, and, furthermore, they will carry extra DNA that is spliced into them.