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 human body.
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 diseases.
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.
Summary: Cloning is the process
of making identical DNA fragments or organisms. DNA cloning involves the
transfer of a DNA fragment from one organism to the same gene. Reproductive
cloning can generate an animal that has the same DNA. The immediate reaction of
the cloning of Dolly was that we could make brand-new copies of ourselves. The
reconstructed egg is treated to stimulate cell division. Therapeutic cloning is
the production of human embryos for use in research. The goal is to harvest
stem cells to treat heart disease, Alzheimer's, cancer and other diseases. They
are important in biomedical research. Recombinant DNA technology is useful to
learn about gene therapy and genetic engineering of organisms. Gene therapy is
used to provide resistance to particular types of disease and genetically
engineer food crops.
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