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Genetic engineering (GE) is the manipulation of genetic material
(ie, DNA or genes) in a cell or an organism in order to produce
desired characteristics and to eliminate unwanted ones. GE
includes a range of different techniques with many different uses,
and can be applied to plants, animals and humans.
For example, the genetic modification of food is a form of GE
that involves manipulating the cells of plants such as maize, to
increase the yields, make it more nutritious and to make it
drought- and disease-resistant.
However, the most contentious type of GE is definitely
related to its applications in humans. GE in humans has
opened up a Pandora’s box of possibilities as it can be used
for both the miraculous and the sinister.
The cloning of Dolly the sheep in 1996 was a very important
event. Until then, the cloning of a human was only possible in
theory. Recent films and TV programmes such as Gattaca, Mutant
X, Dark Angel and books such as Brave New World all focus on possible
consequences of this technology – but what is the real deal?
If you were told that there was a clone of you sitting in the next
room, what would you expect the clone to look and act like?
Probably, exactly the same as you. But, despite all the movies and
TV programmes that have explored the possibility of exact clones,
it is highly unlikely that a clone of you would look exactly the
same and would certainly not act exactly the same.
A clone is not completely genetically identical, as there are
small differences in the genetic make-up just as there are with
identical twins. Despite the fact that identical twins come from
the same egg, after a while one begins to notice the differences
between them in order to tell them apart. It has been discovered
– by doing a number of studies on identical twins brought up in
the same environment – that genes mysteriously react differently
to the same environment.
While cloning a whole human is certainly the ultimate challenge
for genetic engineers, cloning is not limited to this goal.
Cloning can be, and is, done on a much smaller scale and could
involve no more than just the cloning of a single cell.
Therefore, cloning can be divided into two types:
- reproductive cloning (which is the cloning of a whole
organism); and
- therapeutic cloning (which is the cloning of cells or even
organs or other tissue for transplant purposes).
Due to the fact that genetic differences are likely to exist
between a clone and its donor, this uncertainty has led to many
countries banning the reproductive cloning of humans.
Reproductive cloning:
In order to make a clone of someone, one needs a living cell
and a human egg (ovum). The nucleus of the egg, which contains
the DNA, is removed and replaced with the nucleus from the cell
of the person/animal to be cloned.
A short electrical pulse then stimulates the egg to start
dividing and the embryo is then implanted into the womb where
it develops into a duplicate of the person that donated the
cell nucleus. Clones created in this way are not 100% genetically
identical, as there is some DNA from the original egg cell that
is found outside the nucleus (mitochondrial DNA).
Therapeutic cloning and stem cells:
In therapeutic cloning an embryo is created in the same way as
reproductive cloning, but it is not implanted into the womb of a
woman. Instead, stem cells are extracted after the embryo starts
dividing in the first 14 days after fertilisation, which kills the
embryo. Stem cells are special cells with the ability to reproduce
and become one of 300 types of cells, eg, skin, liver cell, hair or
blood cells. These cells are then used to grow the specific type of
tissue or organ that is needed and has the advantage of being
genetically identical to the patient who donated it, eliminating
the problem of organ or tissue rejection. Currently, if someone
has an organ transplant, there is quite a high possibility that
their body will reject the foreign organ and so they not necessary
have to suppress the immune system to lessen the chances of
this happening. Stem cells could potentially be used to repair
damaged or defective tissues around the body, such as the cells
in the pancreas that stop producing insulin in diabetics.
The problem with embryonic stem cells is that many people
feel that by using a human embryo and then killing it, you are
actually killing a potential person. It is for this reason that the
United States and other countries are calling for a global ban on
all human cloning, including the use of embryonic stem cells. As
a result, there has been new research into the potential of what is
known as "adult stem cells".
More than 30 years ago it was discovered that, in addition to
being found in embryos, stem cells are also found in adults.
Adult stem cells can be removed from a person without causing
any harm. Until very recently, it was thought that adult stem
cells were only suitable for cloning a few types of cells and tissues.
However, new studies have found adult stem cells with
almost the same abilities as embryonic stem cells in various
human tissues, including: the spinal cord, the brain, connective
tissue and in the blood of the umbilical cord.
These studies have shown that it is possible for us to manipulate
cells to take on new functions/start doing different jobs
simply by placing them in different environments and "reprogramming"
them. For example, neural (brain) stem cells in mice
have been transformed into the blood stem cells that produce
the different types of blood cells. In other animals, bone marrow
stem cells have become brain cells and liver cells. In humans,
bone marrow stems cells of a patient have been transplanted
into the areas of the heart damaged by a heart attack, triggering
new growth of heart tissue.
Although adult stem cells are already being used successfully
to treat a number of diseases, there are a number of problems
to be overcome, such as finding and extracting the adult stem
cells. Embryonic stem cells have not yet been used for therapy
and research is still in the initial stages. Eventually, it may be
that, rather than just one type, both types of stem cells will be
used for different purposes – whichever proves to be the best
for the situation. In the meantime, parallel research continues
on both cell types. See www.stemcellresearch.org for more information.
Although currently the risks of cloning outweigh the possible
benefits, there are many different potential uses of human
cloning technology:
- Replacing organs and other tissues – such as new skin for
burn victims, brains cells for those with brain damage, spinal
rod cells for the paralysed and complete new organs (hearts,
liver, kidney and lungs). Pigs are also being genetically modified
to make their organs more compatible with humans by
removing the gene that causes rejection. People could have
their appearance changed (cosmetic surgery) using their own
cloned tissue and accident victims and amputees could also
benefit from this tissue regeneration.
- Infertility – human cloning provides couples and individuals
who are unable to have children with another potential option.
- Replacement of a lost child – parents who have lost a child
through an accident or an illness could clone an identical
"replacement" child.
- Creating "donor" people – cloned people could be created to
provide a source of transplant material.
- Gene therapy – cloning technology could be used to prevent,
treat and cure genetic disorders by changing the expression of
a person’s genes. This technology may also provide the cure for
cancer by revealing how cells are switched on and off. Gene
therapy could be used to treat somatic (body) cells where the
change is not passed on to children, or germ (egg and sperm)
cells where the changes are passed on.
- Saving endangered species – by boosting their numbers
through creating clones. However, since clones are almost
genetically identical, the genetic diversity of the species would
not be increased.
- Reversal of the ageing process – once more is understood
about the role that our genes play in the ageing process.
However, some of the above uses carry with them some serious
ethical implications.
Dolly the sheep was created in 1996 using the cloning
methods outlined above. Although Dolly was born looking
normal, she has suffered from several problems
associated with the cloning technique, including premature
arthritis, which is thought to be a side-effect of the cloning.
Other problems with the current cloning techniques, include:
- Low success rate: Dolly the sheep was successfully
cloned, It took 276 unsuccessful attempts before it
worked. Similar work on mice and other mammals has
also produced the same statistics. To date, the success
rate (on animals) is 3-4%.
- Tumours: Embryonic stem cells are unstable and
difficult to control. They have a tendency to uncontrollably
divide leading to tumours/cancer.
- Genetic defects: Although the original DNA from
an embryo is removed and replaced with the nucleus
from the person to be cloned, some DNA from the
original embryo remains in the form of mitochondrial
DNA. This can lead to genetic defects that are not fully
understood and which are only seen in later life.
- Over-growth syndrome: Clones of animals are
larger than average at birth, which can be risky for the
mother.
- Premature ageing: The age of a clone is calculated
by taking its birth age and then adding the age of the
original from which it was cloned. Although Dolly was
born in 1996, she originates from the udder of a sixyear-
old ewe and so her total genetic age is almost 13.
- Massive quantities of human eggs required: If
applied to humans, the current method of cloning would
use a vast number of human eggs. To provide these eggs,
women would have to become "egg factories", and harvesting
them is both painful and dangerous. If adult stem cells
were used, then human eggs would not be required as cells
could be obtained from the patient without harming them.
- Reduction in adaptability: Since, by nature, a clone
is a copy of another person, there would be no unique
genetic combinations introduced into the human gene
pool if human cloning was undertaken on a large scale.
Therefore, if a contagious disease struck for which there
was no cure, all the clones would be wiped out.
- Insertion of the gene: In gene therapy where a
healthy gene can be used to replace a defective gene,
viruses are usually used to insert the gene into the
person’s cells. The virus injects the healthy DNA into
the cells and the genetic defect is corrected. However,
this is not always successful as the virus cannot always
be controlled and has triggered leukaemia in a recent
clinical trial in France.
- Lack of knowledge: Although the Human Genome
Project has mapped out where the different genes are,
a lot more information is needed on their functions.
In some cases, a single gene may have more than one
function, and in others several genes can cause a
genetic disease.
Around the world, different countries have different rules relating
to cloning – some don’t allow reproductive cloning, but do allow
therapeutic cloning, while other countries allow both types.
In South Africa currently, the Human Tissue Act prohibits both therapeutic and reproductive cloning of humans. This situation will change when chapters 6 and 8 of the National Health Act are promulgated - and therapeutic cloning will then be allowed under strict conditions, requiring Ministerial permission, but reproductive cloning on humans will remain strictly prohibited.
In China, there are no laws against cloning either. However,
with the huge population problem and the policy of only one
child per family, there is no interest in reproductive cloning. On
the other hand, there is huge interest in therapeutic cloning and,
as a result, there is a lot of it on the go in China. Some Chinese
cultures believe that humans only become people when they participate
in society – so, according to these cultures, embryos and
foetuses are not considered to be human beings, thereby eliminating
any ethical problems surrounding the creation and
destruction of embryos to get the required stem cells.
The Chinese government is funding extensive research and
drawing back many Chinese scientists from overseas, to undertake
work they would not be allowed to do elsewhere. With easy access
and no limits on obtaining the embryonic material they require, it is
expected that Chinese scientists will race ahead of the rest of the
world in therapeutic cloning technologies.
In the UK there are clear rules banning reproductive cloning, but
scientists in both the UK and Israel are allowed to generate new
embryonic cell lines for therapeutic research. The law in Germany
bans the extraction of stem cells from human embryos for research
within the country, but in 2002 a new law was passed allowing
some human embryonic stem cells to be imported. This means that
German scientists are allowed to undertake work on embryonic
stem cells if they originate from outside Germany.
In the United States there is no public funding for research on
embryonic stem cells. Therefore, although there is no law against therapeutic
cloning in the US, there is almost no public research happening
due to the lack of money and access to the embryonic material. Simultaneously,
an announcement was recently made stating that US public
funds (about US$1,4 million, about R11,2 million) will be provided for
studies using adult stem cells instead of embryonic stem cells.
These different rules for different countries mean that if a scientist
is banned from undertaking cloning in his/her home country, he/she
can simply move to a country where it is allowed. To prevent this
from happening, the US and about 30 other countries want a global
ban on all forms of cloning. However, many countries don’t agree
and thus no progress is being made on implementing this ban.
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