Paper
Cloning and its Impacts on Endangered Species[1]
Lee Jia Huan Amanda (amanda.lee.2012@sis.smu.edu.sg),
1st Year student, Bachelor of Science (Information Systems
Management), School of information Systems
Executive Summary
This paper serves to provide
an introduction to cloning. The possible uses of therapeutic cloning in humans
are explored, but the main focus of the paper is on reproductive cloning. Some of the significant milestones in the
history of cloning are shown, as well as some of the different techniques that
are presently used to clone certain animals, and the risks that cloning
carries. The paper ends off with the possible implications of cloning on
endangered and extinct animals in the future.
Introduction to Cloning
Cloning is the process of creating an organism, or a
part of an organism, from the genetic material that comes solely from one other
organism. The end product of the cloning process would be genetically identical
to the donor. This has profound implications on many issues that the world
faces today.
Future Opportunities
According to United States National Kidney Foundation,
there are 116,680 patients awaiting lifesaving organ transplants, of which 80%
are waiting for kidney transplants. 13 people die each day waiting for a
transplant, and almost 5000 people died waiting for a kidney (2012). All
clearly show that the amount of organ donors is insufficient to meet the needs
of the patients. This is especially so for for kidney transplants, as the
number of patients waiting for a transplant (94,669) far outweighs the number
of transplants that actually took place (16,812). One of the problems
attributed to this situation is the fact that finding suitable donors is not an
easy task. Tissue rejection is a major concern of organ transplants and
cloning, when further developed, might reduce the need for organ donors
entirely. This is because organs can be cloned using the patient’s own cell,
which will not be rejected by the patient’s body since the cloned organ
transplanted will not be seen as a foreign object in the body.
Cloning might also mark the end of the need for
prosthetic limbs in humans and animals. If cloning technology is further
developed, the handicapped may be able to replace their dysfunctional or
missing limbs not with prosthetic limbs, but with limbs that are cloned from
their own cells. Should we be able to replicate the nerves and muscles in our
limbs as well, the handicapped might be able to use the cloned limb as any
other person would.
Another potential application of cloning that is being
explored would be to clone endangered animals. This will ensure that the
species would continue to survive. If this is successful, researchers may also
be able to bring back extinct species, some of whose bodies are preserved in
frozen zoos, where their genetic material is still available.
History of Cloning
Timeline of cloning, according to the Harvard Medical
School:
1962:
John Gurdon claims to have cloned South
African frogs
According to Fatahalian, Schneider and
Reavis (1998), Biologist John Gurdon claimed that he has cloned South African
frogs from the nucleus of differentiated intestinal cells. However, many
scientists remained skeptical of his work, for instance, Dennis Smith found
undifferentiated sex cells in the intestinal tissues of the frogs. Hence, some
of the frogs cloned could have been cloned from the undifferentiated sex cells
rather than from the adult intestinal cell. Although it has never been proven
if Gurdon did manage to clone the frogs, he did manage to generate public
debate on cloning.
1964:
F.C. Steward grew a complete carrot plant from fully differentiated carrot root cells
F.C. Steward grew a complete carrot plant from fully differentiated carrot root cells
1979:
Karl Illmensee claims to have cloned 3 mice
According to Fatahalian, Schneider and
Reavis (1998), Illmensee’s claim came as a surprise at the time, because
researchers were beginning to doubt that mammals could be cloned after many
failures. However, no one has actually seen Illmensee cloning the mice in his
lab, hence it cannot be determined if he did clone the mice.
1984:
Occurrence of the first mammalian cloning,
when Steen Willadsen cloned a sheep from embryonic cells
According to Wilmut, Willadsen found out
that by coating the splitting embryo in a jelly-like casing made from seaweed,
the problem of having the mammalian mother’s immune system destroy the embryo
could be avoided. The technique that Willadsen used can be applied when trying
to save endangered species, since the embryo of the endangered species can be
implanted into the uterus other common subspecies, even after the embryo has
been split. As a result of this, multiple clones can be created at the same
time, limited only by the number of times that the embryo can be split.
1986:
Steen Willadsen and Neal First, Randal
Prather and Willard Eyestone cloned cows from embryonic cells in separate
events
1995:
Ian Wilmut and Keith Campbell cloned two
sheep, Megan and Morag, from cells extracted from differentiated embryos
1996:
Ian Wilmut and Keith Campbell cloned Dolly the
sheep from adult cells
The cloning of Dolly was a major
development in cloning history because she was the first animal to be cloned
from a mammary cell, which is a differentiated cell, via the Roslin technique.
All the other animals cloned before her were cloned from totipotent cells.
Ian Wilmut and Keith Campbell cloned Polly,
a lamb, skin cells
Polly was cloned after Dolly, and is the
first transgenic animal to be cloned. The adult cell that Polly was cloned from
was genetically engineered to contain a human gene. The gene will result in
human proteins being present in the milk that Polly produces. It is hoped that
the human proteins in the milk can be extracted and given to patients who
suffer from hemophilia or bone diseases (CNN, 1997).
1997:
Two Rhesus monkeys were cloned at the Oregan
Regional Primate Center
President Clinton prohibited the use of
federal funds for human cloning
1998:
Ryuzo Yanagimachi cloned fifty mice from
adult cells using the Honolulu Technique
The Honolulu technique is more efficient
than the Roslin technique used to clone Dolly.
2001:
Noah, the bull gaur, was the first
endangered animal to be cloned at the Advanced Cell Technology, Inc.
It was cloned using the nuclear transfer
technique. However, it died from an infection not long after its birth.
2003:
Dolly the sheep was put to sleep after she
suffered from lung cancer and arthritis
Present Situation
There are many
techniques that can be used for cloning. However, the most famous methods are
the somatic cell nuclear transfer (SCNT), the Roslin technique and the Honolulu
technique.
Somatic Cell Nuclear Transfer
The diagrams below show the process of the SCNT:
Figure 1- Diagram showing the process of embryonic
cloning
Source: The Naked Scientists
The genetic material from the haploid egg cell of an
organism is first removed. The nucleus from the diploid donor adult cell is
then isolated and inserted into the egg cell (which now contains no genetic
material) via the process of somatic cell nuclear transfer. An electric shock
is then applied to the egg cell to start the process of cell division and
growth, producing a blastocyst.
Figure 2- Diagram showing the process of making
embryonic stem cells
Source: The Naked Scientists
The cells in the inner cell mass of the blastocyst are
undifferentiated stem cells. These stem cells are extracted from the blastocyst
and placed in a petri dish where the cells further multiply to form an
embryonic stem (ES) cell colony under controlled conditions. As the colony gets
larger, the cells can be split into even smaller colonies and be allowed to
grow on different petri dishes. The blastocyst can be allowed to develop into
an embryo, before it is implanted into the uterus of a female animal.
Roslin Technique
The Roslin technique was developed by the Roslin
Institute. It was made famous after it was used to clone Dolly the sheep. The
technique is a slight variation of the SCNT (Bailey, date unknown). The diagram
below shows the process of the Roslin technique:
Figure 3 – Diagram showing the process of the Roslin
technique
Source: BioInformatics, date
unknown
The Roslin technique was developed by the Roslin
Institute. To clone Dolly the sheep using this technique, mammary cells were
first removed from a Finn Dorset and grown in culture. The nucleus of an ovum
was removed from a Scottish Blackface before an electric shock was applied to
induce the enucleated ovum to fuse with the Finn Dorset mammary cell. The fused
cell was then allowed to develop into an embryo in the tied oviduct of a sheep,
before it was extracted and implanted into a surrogate mother ewe’s womb. The
ewe carried the embryo until it was ready to give birth to Dolly, a Finn
Dorset. Dolly shares the exact same DNA that the mammary cell of the adult Finn
Dorset contained. Megan and Morag, the sheep cloned by Ian Wilmut, were also
cloned using this technique, with the exception that the donor cells used were
embryonic cells (Alvarez-Bautista, 2009).
Honolulu Technique
The Honolulu Technique was developed by the University
of Hawaii, and was used to clone 50 mice. Like the Roslin technique, it is a
variation of the SCNT. The main difference between the Honolulu and the Roslin
technique is that in the Honolulu technique, the donor nucleus is injected
directly into the enucleated egg using a pipette, while an electric pulse is
used to fuse the donor cell and the egg in the Roslin technique. The egg
containing the injected nucleus is then cultured in vitro before it is implanted
into a surrogate mother mouse. With this method, the team led by Ryuzo
Yanagimachi cloned three generations of mice which were all genetically
identical (Alvarez-Bautista, 2009).
Efficiency of the Techniques
The efficiency of SCNT is 0.1-3% (Genetic Science
Learning Center, 2012), while 1 clone is produced out of 277 (0.3%) attempts
for the Roslin technique, and 3 out of 100 (3%) for the Honolulu technique
(Fatahalian, Schneider and Reavis, 1998). This makes the Honolulu technique
more efficient than the Roslin technique.
Challenges Faced in Cloning
Large Offspring Syndrome
Many clones have the large offspring syndrome (LOS),
as they are larger at birth as compared to the animals of natural birth. The
clones with the LOS also have larger organs, which may cause breathing and
blood flow problems (Genetic Science Learning Center, 2012).
Abnormal Gene Expression
Clones that were cloned from adult cells may not
express genes the way that a natural animal would if the cell from which the
animal was cloned from might not have been reprogrammed properly by the
scientist. Differentiated cells need to be coaxed into its undifferentiated
state before the cell can express its genes properly (Genetic Science Learning
Center, 2012). Researchers at the Whitehead Institute for Biomedical Research
in Cambridge, Massachusetts have found that about 4% of the genes in cloned
mice function abnormally, not because of mutations, but because of abnormal
activation and expression of the genes (U.S.
Department of Energy, 2009).
End-Replication Problem
With every cell division, the chromosomes in the cell
become shorter due to the naturally-occurring end-replication problem. The
shortening of the telomeres is responsible for the ageing process. Animals with
shorter telomeres will age faster than those with longer telomeres. However,
the effect of this problem is unclear, since cloned cattle and mice had longer
telomeres than their natural counterparts, while Dolly the sheep has shorter
telomeres (Genetic Science Learning Center, 2012). However, there is little
data about how clones age since many of them do not live long enough (U.S. Department of Energy, 2009).
Health of the Clones
Clones seem to be more susceptible to infections,
tumor growths and other diseases. Studies have shown that cloned mice have poor
health and die early. Clones have also been known to die with no apparent cause
(U.S. Department of Energy, 2009). The DNA of
the clone will also deteriorate over time, and an accumulation of the damages
may result in the clone having cancer (BioInformatics, date unknown).
Future Considerations
About 100 species becomes extinct each day (Lanza et
al., 2000). With cloning, there is a possibility that endangered species can be
saved. However, the ability to clone the endangered species does not solve the
root cause of the problem, which is the changing environment and human
behavior. The reason why the animals are endangered is because the current
environment is not suitable for them to live in, either due to the loss of
their natural habitat, or because they are constantly being hunted. While
cloning can ensure that the species survives, there is no guarantee that the
cloned animals will continue to survive well outside of the controlled
environment in which they were cloned.
The cloning of endangered animals might potentially
marginalize the need and effort put into wildlife conservation. This might
happen if people start to think that endangered species can simply be restored
by cloning, and hence not feel the need to protect the habitats of the animals.
Perhaps it would be wise to put more effort into conserving the natural habitat
of animals instead of trying to clone the animals when they are endangered.
According to Darwin’s Theory of Evolution, “It is not
the strongest of the species that survives, nor the most intelligent; it is the
one that is most adaptable to change.” If the animals are not able to adapt to
the changing environment, then they would not survive. Trying to clone the
endangered animals might lead to humans disrupting the natural flow of things.
If cloning can save the endangered animals, it might
be possible to revive and restore the extinct species. This can be done by
taking the genetic material of animals preserved in the frozen zoos. However,
there is much that we do not know about the extinct species, such as their
behavior, diet and habitat. Hence, bringing these animals back to life may
bring about unforeseen circumstances.
Conclusion
There is still a lot more to learn about cloning, and
the problems that clones might face throughout their lifespans are still
unclear. There may also be other problems that come with cloning endangered
species that are still unclear. Cloning these animals may even cause more
suffering for the clones.
However, cloning still has limitless potential in
terms of solving other problems that we face, such as the need for organs, and
the problem of tissue rejection. It may also be helpful in trying to fight
diseases in humans and animals. Hence, cloning technology should still be
developed, but with prudence, and both the government and the scientists have
the responsibility to regulate the use of cloning.
References
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