Cloning
Sham S. Misri
Cloning is the process of creating an identical copy of an original. The
word ‘clone’ was coined by the British geneticist J.B.S. Haldane in 1963, and
is derived from the Greek word for "twig".
Steps:
A non reproductive cell (e.g. Muscle cell) is extracted from the body of
a person to be cloned.
The cell is starved into a state of hibernation by placing it in a salt
solution containing just enough nutrients to keep it alive.
The cell stops dividing and the genes in the DNA are reprogrammed so
that the cell behaves like an embryo cell.
The cell is fertilized with an egg in vitro whose nucleus has been
removed and allowed to multiply till 32 cell stage.
The embryo is finally placed in a womb and the child born will be
genetically identical.
A clone in the biological sense is a multi-cellular organism that is
genetically identical to another living organism.
In biology, cloning is used in two contexts: cloning a gene, or cloning
an organism. Cloning a gene means to extract a gene from one organism (for
example, by Polymerase Chain Reaction, PCR*) and to insert it into a second
organism (usually via a vector**), where it can be used and studied. Cloning a
gene sometimes can refer to success in identifying a gene associated with some
phenotype. For example, when biologists say that the gene for disease X has
been cloned, they mean that the gene's location and DNA sequence has been
identified, although the ability to specifically copy the physical DNA is a
side-effect of its identification.
Cloning an organism means to create a new organism with the same genetic
information as an existing one. This can be done by somatic cell nuclear
transfer in which the nucleus is removed from an egg cell and replaced with a
nucleus extracted from a cell of the organism to be cloned (currently, both the
egg cell and its transplanted nucleus must be from the same species). As the
nucleus contains (almost) all of the genetic information of a life form, the
"host" egg cell will develop into an organism genetically identical
to the nucleus "donor".
This technique has been successfully performed on several species, such
as frogs, mice, sheep, and cattle (the most famous example being the sheep
"Dolly"). However the success rate is very low, Dolly was born after
276 failed attempts; 70 calves have been created from 9,000 attempts and one
third of them died young. With certain species such as dogs, rats and horses no
successful clones have been created at all. Many people believe that attempts
to perform human cloning would be unethical, but some scientists have publicly
announced their intention to do so. Some believe the Chinese may have already
done so.
A surprising development to do with aging resulted from finds that Dolly
was apparently born old; she developed arthritis at age six. Aging of this type
is thought to be due to telomeres, regions at the tips of chromosomes which
prevent genetic threads fraying every time a cell divides. Over time telomeres
get worn down until cell-division is no longer possible - this is thought to be
a cause of aging. However, when researchers cloned cows they appeared to be
younger than they should be. Analysis of the cow's telomeres showed they had
not only been 'reset' to birth-length, but they were actually longer -
suggesting these clones would live longer life spans than normal cows (but many
have died young after excessive growth). Researchers think that this could
eventually be developed to reverse aging in humans.
Human cloning
Human cloning is a subject of great controversy regarding its ethical
and practical consequences. A number of groups have made claims that they are
working on or have already produced human clones. None of these claims has
perhaps been independently confirmed.
*Polymerase Chain Reaction (PCR) is a molecular biological method for
amplifying (creating multiple copies of) DNA without using a living organism,
such as E. coli or yeast. PCR is commonly used in medical and biological
research labs for a variety of tasks, such as the detection of hereditary
diseases, the identification of genetic fingerprints, the cloning of genes, and
paternity testing.
**Vector
In biology, a vector is a means to transmit genetic information or whole
organisms (usually pathogens) between other organisms. Viruses, for example,
are considered as vectors because they spread by introducing their genetic
information into their hosts. Vectors are becoming more common and powerful
tools of research as the human genome and genomes of other organisms are being
extensively studied.
