Cloning is the process of making an identical copy of something. It refers
to processes used to create copies of DNA fragments, be it molecular cloning
or cell cloning or organisms. The term also covers when organisms such as
bacteria, insects or plants reproduce asexually.
The possibility of human
cloning was raised when scientists at Roslin Institute created the
much-celebrated sheep called Dolly. It aroused worldwide interest and
concern because of its scientific and ethical implications. The immediate
reaction was that humans would now be able to make brand-new copies of
themselves. This breakthrough in 1997 also generated uncertainty over the
meaning of cloning'. There are three types of cloning. They are DNA cloning,
reproductive cloning and therapeutic cloning.
Recombinant DNA technology or DNA cloning involves the transfer of a DNA
fragment from one organism to a self-replicating genetic element. Scientists
studying a particular gene often use bacterial plasmids to generate multiple
copies of the same gene. Plasmids are self-replicating extra-chromosomal
circular DNA molecules. When the fragment of the chromosomal DNA is joined
with its cloning vector in the lab, it is called a recombinant DNA molecule.
Reproductive cloning is a technology used to generate an animal that has
the same nuclear DNA as another currently or previously existing animal.
Dolly was created by this type of cloning technology. In the process,
scientists transfer genetic material from the nucleus of a donor adult cell
to an egg whose genetic material has been removed. The reconstructed egg
containing the DNA from a donor cell must be treated with chemicals or
'electric current to stimulate cell division. Once the cloned embryo reaches
a suitable stage, it is transferred to the uterus of a female host where it
continues to develop until birth.
Therapeutic cloning is also called `embryo cloning'. It is the production
of human embryos for use in research. The goal of this process is not to
create cloned human beings but rather to harvest stem cells that can be used
to treat disease. Stem cells are important to biomedical researchers because
they can be used to generate virtually any type of specialised cell in the
Stem cells are extracted from the egg after it has divided for five days.
The extraction process destroys the embryo, which raises a variety of
ethical concerns. It is hoped that one day, stem cells can be used to serve
as replacement cells to treat heart disease, Alzheimer's, cancer and other
Recombinant DNA technology is useful for learning about other related
technologies such as gene therapy and genetic engineering of organisms. Gene
therapy can be used to treat certain genetic conditions by introducing virus
vectors that transfer corrected copies of faulty genes into the cells of a
host organism. Similarly, genes from different organisms can be used to
improve taste and nutritional value or provide resistance to particular
types of disease or genetically engineer food crops.