In biology a clone is 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 word clone has
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 that constitute a 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 DNA vector
(carrier). The most commonly used vectors are plasmids (circular DNA
molecules that originated from bacteria), viruses, and yeast cells.
Plasmids are not a part of the main cellular genome, but they can carry genes
that provide the host cell with useful properties, such as drug 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.
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