Тема: Genetic Engineering
Вид реферата: реферат
Формат: Microsoft Word документ
Сжатие: ZIP архив
Создан: 23 мая 2007 года
All that we are is the result of what we have thought
For what shall it profit a man, if he shall gain the whole world and lose his own soul?
While plant biotechnology has been used for centuries to enhance plants,
microorganisms and animals for food, only recently has it allowed for the
transfer of genes from one organism to another. Yet there is now a
widespread controversy over the harmful and beneficial effects of genetic
engineering to which, at this time, there seems to be no concrete solution.
The ideas below are expected to bring in a bit of clearance into the topic.
Here I’m going to reveal some facts concerning genetic engineering,
specially the technology, its weak and strong points (if any). Probably the
information brought is a bit too prejudiced, for I’m certainly not in favor
of making jokes with nature, but I really tried to find some good things
What is genetic engineering?
Genetic engineering is a laboratory technique used by scientists to change
the DNA of living organisms.
DNA is the blueprint for the individuality of an organism. The organism
relies upon the information stored in its DNA for the management of every
biochemical process. The life, growth and unique features of the organism
depend on its DNA. The segments of DNA which have been associated with
specific features or functions of an organism are called genes.
Molecular biologists have discovered many enzymes which change the
structure of DNA in living organisms. Some of these enzymes can cut and
join strands of DNA. Using such enzymes, scientists learned to cut specific
genes from DNA and to build customized DNA using these genes. They also
learned about vectors, strands of DNA such as viruses, which can infect a
cell and insert themselves into its DNA.
With this knowledge, scientists started to build vectors which incorporated
genes of their choosing and used the new vectors to insert these genes into
the DNA of living organisms. Genetic engineers believe they can improve the
foods we eat by doing this. For example, tomatoes are sensitive to frost.
This shortens their growing season. Fish, on the other hand, survive in
very cold water. Scientists identified a particular gene which enables a
flounder to resist cold and used the technology of genetic engineering to
insert this 'anti-freeze' gene into a tomato. This makes it possible to
extend the growing season of the tomato.
At first glance, this might look exciting to some people. Deeper
consideration reveals serious dangers.
There are 4 types of genetic engineering which consist of recombinant
engineering, microinjection, electro and chemical poration, and also
The first of the 4, recombinant engineering, is also known as r-DNA
technology. This technology relies on biological vectors such as plasmids
and viruses to carry foreign genes into cells. The plasmids are small
circular pieces of genetic material found in bacteria that can cross
species boundaries. These circular pieces can be broken, which results with
an addition of a new genetic material to the broken plasmids. The plasmids,
now joined with the new genetic material, can move across microbial cell
boundaries and place the new genetic material next to the bacterium's own
genes. After this takes place, the bacteria will then take up the gene and
will begin to produce the protein for which the gene codes. In this
technique, the viruses also act as vectors. They are infectious particles
that contain genetic material to which a new gene can be added. Viruses
carry the new gene into a recipient cell driving the process of infecting
that cell. However, the viruses can be disabled so that when it carries a
new gene into a cell, it cannot make the cell reproduce or make copies of
The next type of genetic engineering is referred to as microinjection. This
technique does not rely on biological vectors, as does r-DNA. It is
somewhat of a simple process. It is the injecting of genetic material
containing the new gene into the recipient cell. Where the cell is large
enough, injection can be done with a fine-tipped glass needle. The injected
genes find the host cell genes and incorporate themselves among them.
Electro and chemical poration
This technique is a direct gene transfer involving creating pores or holes
in the cell membrane to allow entry of the new genes. If it is done by
bathing cells in solutions of special chemicals, then it is referred to as
chemical poration. However, if it goes through subjecting cells to a weak
electric current, it is called electroporation.
This last technique is a projectile method using metal slivers to deliver
the genetic material to the interior of the cell. These small slivers,
which must be smaller than the diameter of the target cell, are coated with
genetic material. The coated slivers are propelled into the cells using a
shotgun. After this has been done, a perforated metal plate stops the shell
cartridge but still allows the slivers to pass through and into living
cells on the other side. Once inside, the genetic material is transported
to the nucleus where it is incorporated among host cells.
The history of GE
The concept was first introduced by an Australian monk named Gregor Mendel
in the 19th century. His many experiments cemented a foundation for future
scientists and for the founding concepts in the study of genetics.
Throughout Mendel's life, he was a victim of criticism and ridicule by his
fellow monks for his "foolish" experiments. It took 35 years until he was
recognized for his experiments and known for the selective breeding
process. Mendel's discoveries made scientists wonder how information was
transferred from parent to offspring and whether the information could be
captured and/or manipulated.
James D. Watson and Francis H. C. Crick were curious scientists who later
became known as the founding fathers of genetic engineering.
Watson and Crick wanted to determine how genetic blueprints are determined
and they also proposed that DNA structures are genetic messengers or that
chemical compounds of proteins and amino acids all come together as a way
to rule out characteristics and traits. These 2 scientists produced a code
of DNA and thus answered the question of how characteristics are
determined. They also established that DNA are the building blocks of all
Selective breeding and genetic engineering
Selective breeding and genetic engineering are "both used for the
improvement of human society." However, selective breeding is a much longer
and more expensive process than genetic engineering. It takes genetic
engineering only one generation of offspring to see and study improvement
as opposed to selective breeding where many generations are necessary.
Therefore, it costs more to observe many generations.
Selective breeding is known as the natural way to engineer genes while
genetic engineering is more advanced, technical, scientific, complex and is
inevitable in out future.
What are the dangers?
Many previous technologies have proved to have adverse effects unexpected
by their developers. DDT, for example, turned out to accumulate in fish and
thin the shells of fish-eating birds like eagles and ospreys. And
chlorofluorocarbons turned out to float into the upper atmosphere and
destroy ozone, a chemical that shields the earth from dangerous radiation.
What harmful effects might turn out to be associated with the use or
release of genetically engineered organisms?
This is not an easy question. Being able to answer it depends on
understanding complex biological and ecological systems. So far, scientists
know of no generic harms associated with genetically engineered organisms.
For example, it is not true that all genetically engineered foods are toxic
or that all released engineered organisms are likely to proliferate in the
environment. But specific engineered organisms may be harmful by virtue of
the novel gene combinations they possess. This means that the risks of
genetically engineered organisms must be assessed case by case and that
these risks can differ greatly from one gene-organism combination to
So far, scientists have identified a number of ways in which genetically
engineered organisms could potentially adversely impact both human health
and the environment. Once the potential harms are identified, the question
becomes how likely are they to occur. The answer to this question falls
into the arena of risk assessment.
In addition to posing risks of harm that we can envision and attempt to
assess, genetic engineering may also pose risks that we simply do not know
enough to identify. The recognition of this possibility does not by itself
justify stopping the technology, but does put a substantial burden on those
who wish to go forward to demonstrate benefits.
Fundamental Weaknesses of the Concept
Imprecise Technology—A genetic engineer moves genes from one organism to
another. A gene can be cut precisely from the DNA of an organism, but the
insertion into the DNA of the target organism is basically random. As a
consequence, there is a risk that it may disrupt the functioning of other
genes essential to the life of that organism. (Bergelson 1998)
Side Effects—Genetic engineering is like performing heart surgery with a
shovel. Scientists do not yet understand living systems completely enough
to perform DNA surgery without creating mutations which could be harmful to
the environment and our health. They are experimenting with very delicate,
yet powerful forces of nature, without full knowledge of the repercussions.
(Washington Times 1997)
Widespread Crop Failure—Genetic engineers intend to profit by patenting
genetically engineered seeds. This means that, when a farmer plants
genetically engineered seeds, all the seeds have identical genetic
structure. As a result, if a fungus, a virus, or a pest develops which can
attack this particular crop, there could be widespread crop failure.
Threatens Our Entire Food Supply—Insects, birds, and wind can carry
genetically altered seeds into neighboring fields and beyond. Pollen from
transgenic plants can cross-pollinate with genetically natural crops and
wild relatives. All crops, organic and non-organic, are vulnerable to
contamination from cross-pollinatation. (Emberlin 1999)
Here are the some examples of the potential adverse effects of genetically
engineered organisms may have on human health. Most of these examples are
associated with the growth and consumption of genetically engineered crops.
Different risks would be associated with genetically engineered animals
and, like the risks associated with plants, would depend largely on the new
traits introduced into the organism.
New Allergens in the Food Supply
Transgenic crops could bring new allergens into foods that sensitive
individuals would not know to avoid. An example is transferring the gene
for one of the many allergenic proteins found in milk into vegetables like
carrots. Mothers who know to avoid giving their sensitive children milk
would not know to avoid giving them transgenic carrots containing milk
proteins. The problem is unique to genetic engineering because it alone can
transfer proteins across species boundaries into completely unrelated
Genetic engineering routinely moves proteins into the food supply from
organisms that have never been consumed as foods. Some of those proteins
could be food allergens, since virtually all known food allergens are
proteins. Recent research substantiates concerns about genetic engineering
rendering previously safe foods allergenic. A study by scientists at the
University of Nebraska shows that soybeans genetically engineered to
contain Brazil-nut proteins cause reactions in individuals allergic to
Scientists have limited ability to predict whether a particular protein
will be a food allergen, if consumed by humans. The only sure way to
determine whether protein will be an allergen is through experience. Thus
importing proteins, particularly from nonfood sources, is a gamble with
respect to their allergenicity.
Genetic engineering often uses genes for antibiotic resistance as
"selectable markers." Early in the engineering process, these markers help
select cells that have taken up foreign genes. Although they have no
further use, the genes continue to be expressed in plant tissues. Most
genetically engineered plant foods carry fully functioning antibiotic-
The presence of antibiotic-resistance genes in foods could have two harmful
effects. First, eating these foods could reduce the effectiveness of
antibiotics to fight disease when these antibiotics are taken with meals.
Antibiotic-resistance genes produce enzymes that can degrade antibiotics.
If a tomato with an antibiotic-resistance gene is eaten at the same time as
an antibiotic, it could destroy the antibiotic in the stomach.
Second, the resistance genes could be transferred to human or animal
pathogens, making them impervious to antibiotics. If transfer were to
occur, it could aggravate the already serious health problem of antibiotic-
resistant disease organisms. Although unmediated transfers of genetic
material from plants to bacteria are highly unlikely, any possibility that
they may occur requires careful scrutiny in light of the seriousness of
In addition, the widespread presence of antibiotic-resistance genes in
engineered food suggests that as the number of genetically engineered
products grows, the effects of antibiotic resistance should be analyzed
cumulatively across the food supply.
Production of New Toxins
Many organisms have the ability to produce toxic substances. For plants,
such substances help to defend stationary organisms from the many predators
in their environment. In some cases, plants contain inactive pathways
leading to toxic substances. Addition of new genetic material through
genetic engineering could reactivate these inactive pathways or otherwise
increase the levels of toxic substances within the plants. This could
happen, for example, if the on/off signals associated with the introduced
gene were located on the genome in places where they could turn on the
previously inactive genes.
Concentration of Toxic Metals
Some of the new genes being added to crops can remove heavy metals like
mercury from the soil and concentrate them in the plant tissue. The purpose
of creating such crops is to make possible the use of municipal sludge as
fertilizer. Sludge contains useful plant nutrients, but often cannot be
used as fertilizer because it is contaminated with toxic heavy metals. The
idea is to engineer plants to remove and sequester those metals in inedible
parts of plants. In a tomato, for example, the metals would be sequestered
in the roots; in potatoes in the leaves. Turning on the genes in only some
parts of the plants requires the use of genetic on/off switches that turn
on only in specific tissues, like leaves.
Such products pose risks of contaminating foods with high levels of toxic
metals if the on/off switches are not completely turned off in edible
tissues. There are also environmental risks associated with the handling
and disposal of the metal-contaminated parts of plants after harvesting.
Enhancement of the Environment for Toxic Fungi
Although for the most part health risks are the result of the genetic
material newly added to organisms, it is also possible for the removal of
genes and gene products to cause problems. For example, genetic engineering
might be used to produce decaffeinated coffee beans by deleting or turning
off genes associated with caffeine production. But caffeine helps protect
coffee beans against fungi. Beans that are unable to produce caffeine might
be coated with fungi, which can produce toxins. Fungal toxins, such as
aflatoxin, are potent human toxins that can remain active through processes
of food preparation.
No Long-Term Safety Testing
Genetic engineering uses material from organisms that have never been part
of the human food supply to change the fundamental nature of the food we
eat. Without long-term testing no one knows if these foods are safe.
Decreased Nutritional Value
Transgenic foods may mislead consumers with counterfeit freshness. A
luscious-looking, bright red genetically engineered tomato could be several
weeks old and of little nutritional worth.
Problems Cannot Be Traced
Without labels, our public health agencies are powerless to trace problems
of any kind back to their source. The potential for tragedy is staggering.
Side Effects can Kill
37 people died, 1500 were partially paralyzed, and 5000 more were
temporarily disabled by a syndrome that was finally linked to tryptophan
made by genetically-engineered bacteria.
As with any new technology, the full set of risks associated with genetic
engineering have almost certainly not been identified. The ability to
imagine what might go wrong with a technology is limited by the currently
incomplete understanding of physiology, genetics, and nutrition.
Potential Environmental Harms
One way of thinking generally about the environmental harm that genetically
engineered plants might do is to consider that they might become weeds.
Here, weeds means all plants in places where humans do not want them. The
term covers everything from Johnson grass choking crops in fields to kudzu
blanketing trees to melaleuca trees invading the Everglades. In each case,
the plants are growing unaided by humans in places where they are having
unwanted effects. In agriculture, weeds can severely inhibit crop yield. In
unmanaged environments, like the Everglades, invading trees can displace
natural flora and upset whole ecosystems.
Some weeds result from the accidental introduction of alien plants, but
many were the result of purposeful introductions for agricultural and
horticultural purposes. Some of the plants intentionally introduced into
the United States that have become serious weeds are Johnson grass,
multiflora rose, and kudzu. A new combination of traits produced as a
result of genetic engineering might enable crops to thrive unaided in the
environment in circumstances where they would then be considered new or
worse weeds. One example would be a rice plant engineered to be salt-
tolerant that escaped cultivation and invaded nearby marine estuaries.
Gene Transfer to Wild or Weedy Relatives
Novel genes placed in crops will not necessarily stay in agricultural
fields. If relatives of the altered crops are growing near the field, the
new gene can easily move via pollen into those plants. The new traits might
confer on wild or weedy relatives of crop plants the ability to thrive in
unwanted places, making them weeds as defined above. For example, a gene
changing the oil composition of a crop might move into nearby weedy
relatives in which the new oil composition would enable the seeds to
survive the winter. Overwintering might allow the plant to become a weed or
might intensify weedy properties it already possesses.
Change in Herbicide Use Patterns
Crops genetically engineered to be resistant to chemical herbicides are
tightly linked to the use of particular chemical pesticides. Adoption of
these crops could therefore lead to changes in the mix of chemical
herbicides used across the country. To the extent that chemical herbicides
differ in their environmental toxicity, these changing patterns could
result in greater levels of environmental harm overall. In addition,
widespread use of herbicide-tolerant crops could lead to the rapid
evolution of resistance to herbicides in weeds, either as a result of
increased exposure to the herbicide or as a result of the transfer of the
herbicide trait to weedy relatives of crops. Again, since herbicides differ
in their environmental harm, loss of some herbicides may be detrimental to
the environment overall.
Squandering of Valuable Pest Susceptibility Genes
Many insects contain genes that render them susceptible to pesticides.
Often these susceptibility genes predominate in natural populations of
insects. These genes are a valuable natural resource because they allow
pesticides to remain as effective pest-control tools. The more benign the
pesticide, the more valuable the genes that make pests susceptible to it.
Certain genetically engineered crops threaten the continued susceptibility
of pests to one of nature's most valuable pesticides: the Bacillus
thuringiensis or Bt toxin. These "Bt crops" are genetically engineered to
contain a gene for the Bt toxin. Because the crops produce the toxin in
most plant tissues throughout the life cycle of the plant, pests are
constantly exposed to it. This continuous exposure selects for the rare
resistance genes in the pest population and in time will render the Bt
pesticide useless, unless specific measures are instituted to avoid the
development of such resistance.
Addition of foreign genes to plants could also have serious consequences
for wildlife in a number of circumstances. For example, engineering crop
plants, such as tobacco or rice, to produce plastics or pharmaceuticals
could endanger mice or deer who consume crop debris left in the fields
after harvesting. Fish that have been engineered to contain metal-
sequestering proteins (such fish have been suggested as living pollution
clean-up devices) could be harmful if consumed by other fish or raccoons.
Creation of New or Worse Viruses
One of the most common applications of genetic engineering is the
production of virus-tolerant crops. Such crops are produced by engineering
components of viruses into the plant genomes. For reasons not well
understood, plants producing viral components on their own are resistant to
subsequent infection by those viruses. Such plants, however, pose other
risks of creating new or worse viruses through two mechanisms:
recombination and transcapsidation.
Recombination can occur between the plant-produced viral genes and closely
related genes of incoming viruses. Such recombination may produce viruses
that can infect a wider range of hosts or that may be more virulent than
the parent viruses.
Transcapsidation involves the encapsulation of the genetic material of one
virus by the plant-produced viral proteins. Such hybrid viruses could
transfer viral genetic material to a new host plant that it could not
otherwise infect. Except in rare circumstances, this would be a one-time-
only effect, because the viral genetic material carries no genes for the
foreign proteins within which it was encapsulated and would not be able to
produce a second generation of hybrid viruses.
Gene Pollution Cannot Be Cleaned Up
Once genetically engineered organisms, bacteria and viruses are released
into the environment it is impossible to contain or recall them.
Unlike chemical or nuclear contamination, negative effects are
DNA is actually not well understood.
Yet the biotech companies have already planted millions of acres with
genetically engineered crops, and they intend to engineer every crop in the
The concerns above arise from an appreciation of the fundamental role DNA
plays in life, the gaps in our understanding of it, and the vast scale of
application of the little we do know. Even the scientists in the Food and
Drug administration have expressed concerns.
As with human health risks, it is unlikely that all potential harms to the
environment have been identified. Each of the potential harms above is an
answer to the question, "Well, what might go wrong?" The answer to that
question depends on how well scientists understand the organism and the
environment into which it is released. At this point, biology and ecology
are too poorly understood to be certain that question has been answered
Certainly, there should be some. Still, most of them are connected with
commercial gains for genetic engineering companies. A popular claim, that
farmers will benefit, is simply not true. It is just the same thing with
consumers. No one is going to feed the poorest with GE products for the
famine in many underdeveloped countries is simply the matter of inability
to buy food, not lack of it. So today, at the present stage of development,
we hardly need GE expanding on food products, needless to say about animal
and human cloning. Incidentally, some daydreaming proponents of GE really
believe that mankind will not be able to survive without it. According to
them, we will certainly have to genetically upgrade ourselves in response
to governmental activities. The humans will be able to hibernate – just
like some animals – to cover long distances without aging, and, probably,
will become immortal…
Still, what about the present need of GE? Where can GE particularly be used
now without a threat to the humans and the environment?
So, scientists say that genetic engineering can make it possible to battle
disease (cancer, in particular), disfigurement, and other maladies through
a series of medical breakthroughs that will be beneficial to the human
race. Moreover, cloning will be able to end the extinction of many
endangered species. The main question is whether we can trust genetic
engineering. The fact is that even genetically changed corn is already
The recent research showed that pollen from genetically engineered corn
plants is toxic to monarch butterflies. Corn plants produce huge quantities
of pollen, which dusts the leaves of plants growing near corn fields. Close
to half the monarch caterpillars that fed on milkweed leaves dusted with Bt
corn pollen died. Surviving caterpillars were about half the size of
caterpillars that fed on leaves dusted with pollen from non-engineered
corn. Something is wrong with the engineered products – they are different,
so we cannot be sure about the effect they will bring about.
So, is the technology trustworthy? I suppose not.
So, do we need it? There are far too many disadvantages of GE and far too
many unpredictable things may happen. The humans are amateurs in this area,
in fact, they are just like a monkey taught to press PC buttons. We have
almost no experience, the technology has not yet evolved enough. I believe,
we should wait, otherwise we may give birth to a trouble, which would be
impossible to resolve.
1. David Heaf ‘Pros and Cons of Genetic Engineering’, 2000, ifgene;
2. Ricarda Steinbrecher, 'From Green to Gene Revolution', The
Vol 26 No 6;
3. ‘Genetic Engineering Kills Monarch Butterflies’, Nature Magazine, May
4. ‘Who's Afraid of Genetic Engineering?’ The New York Times August 26,
5. Sara Chamberlain ‘Techno-foods’, August 19, 1999, The New
6. W French Anderson, 'Gene Therapy' in Scientific American, September
7. Nature Biotechnology Vol 14 May 1996;
8. Andrew Kimbrell 'Breaking the Law of Life' in Resurgence May/June 1997
9. Jim Hightower ‘What’s for dinner?’, May 29, 2000.
What is genetic engineering? 1
The history of GE 2
Selective breeding and genetic engineering 3
What are the dangers? 3
Fundamental Weaknesses of the Concept 3
Health Hazards 4
Potential Environmental Harms 6
Any pros? 8