Genetic
Engineering - alteration of an organism's genetic, or hereditary,
material to eliminate undesirable characteristics or to produce desirable
new ones. Genetic engineering is used to increase plant and animal
food production; to diagnose disease, improve medical treatment, and
produce vaccines and other useful drugs; and to help dispose of industrial
wastes. Included in genetic engineering techniques are the selective
breeding of plants and animals, hybridization (reproduction between
different strains or species), and recombinant deoxyribonucleic acid
(DNA).
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History of Genetic Engineering
Prehistoric
times to 1900
Gatherers
find food from plants they find in nature, and farmers plant seeds
saved from domesticated crops. Foods are manipulated through the use
of yeast and fermentation. Some naturalists and farmers begin to recognize
"hybrids," plants produced through natural breeding between
related varieties of plants.
1900
European plant scientists begin using Gregor Mendel's genetic theory
to manipulate and improve plant species. This is called "classic
selection." A plant of one variety is crossed with a related
plant to produce desired characteristics.
Modern
genetic engineering
1953
James Watson and Francis Crick publish their discovery of the three-dimensional
double helix structure of DNA. This discovery will eventually lead
to the ability of scientists to identify and "splice" genes
from one kind of organism into the DNA of another.
1973
Herbert Boyer and Stanley Cohen combine their research to create the
first successful recombinant DNA organism.
1980
The U.S. Supreme Court in Diamond v. Chakrabarty rules that genetically
altered life forms can be patented. The decision allows the Exxon
Oil Company to patent an oil-eating microorganism.
1982
The U.S. Food and Drug Administration approves the first genetically
engineered drug, Genentech's Humulin, a form of human insulin produced
by bacteria. This is the first consumer product developed through
modern bioengineering.
1986
The first field tests of genetically engineered plants (tobacco) are
conducted in Belgium.
1987
The first field tests of genetically engineered crops (tobacco and
tomato) are conducted in the United States.
1992
Calgene's Favr Savr tomato, engineered to remain firm for a longer
period of time, is approved for commercial production by the US Department
of Agriculture.
1992
The FDA declares that genetically engineered foods are "not inherently
dangerous" and do not require special regulation.
1994
The European Union's first genetically engineered crop, tobacco, is
approved in France.
2000
International Biosafety Protocol is approved by 130 countries at the
Convention on Biological Diversity in Montréal, Canada. The
protocol agrees upon labeling of genetically engineered crops, but
still needs to be ratified by 50 nations before it goes into effect.
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II.
SELECTIVE BREEDING AND HYBRIDIZATION
SELECTIVE
BREEDING
The first
genetic engineering technique, still used today, was the selective
breeding of plants and animals, usually for increased food production.
In selective breeding, only those plants or animals with desirable
characteristics are chosen for further breeding. Corn has been selectively
bred for increased kernel size and number and for nutritional content
for about 7,000 years. More recently, selective breeding of wheat
and rice to produce higher yields has helped supply the world's ever-increasing
need for food.Cattle
and pigs were first domesticated about 8,000 years ago and through
selective breeding have become main sources of animal food for humans.
Dogs and horses have been selectively bred for thousands of years
for work and recreational purposes, resulting in more than 130 different
dog breeds and 100 different horse breeds.
HYBRIDIZATION
Hybridization
(cross-breeding) may involve combining different strains of a species
(that is, members of the same species with different characteristics)
or members of different species in an effort to combine the most desirable
characteristics of both. For at least 3,000 years, female horses have
been bred with male donkeys to produce mules, and male horses have
been bred with female donkeys to produce hinnies, for use as work
animals.
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III.
RECOMBINANT DNA
What
is DNA?
Deoxyribonucleic
Acid (DNA)
-is a smaller chemical units called nucleotides which is compose
of:
-a sugar known as deoxyribose
-an oxygenated phosphorus chemical group called phosphate
-nitrogen containing compound known as base
-it has four bases:
adenine(A)
guanine (G)
Thymine(T)
Cytosine (C)
DNA is consist of two chains
that coil around each other in shape called a double helix
Which resembles a twisted ladder consist of the link sugars and phosphates
of the nucleotides.Each rung is made up of two paireds bases (A-T)
(G-C).The order of the bases or the base sequence, provides the information
necessary for a cell to make a specific protein.The form and function
of the cell depends on the proteins it produces.Thus the base sequence
of an organism’s DNA make the organism different from all other
living things..
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Techniques
In this technique,a gene- sized fragment of DNA is taken
from one organism and joined to a DNA molecule from another organism
or from the same organism.Gene-sized DNA fragments are isolated
by means of restriction enzymes.This enzymes react chemically with
a specific base sequence in the DNA molecule and break the moleculeat
at that point.This point is called the cleavage site.The gene-sized
DNA fragment can then be spliced (joined) to a DNA molecule by using
an enzyme called ligase. The hybrid molecule formed is called recombinant
DNA.
When recombinant DNA is mixed with specially prepared cells , a
few of the cell will take up a hybrid molecule in a process of transformation.The
mixture of cells is then placed to a special culture medium that
that allows only to transform cells to grow.Each of the transformed
cells with the newly added genetic information grows overnight into
a colony of millions of cells. This colony represents a clone-that
is, a group of genitically identical cells.
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Food Production
Recombinant DNA has been used to combat one of the greatest
problems in plant food production: the destruction of crops by plant
viruses. For example, by transferring the protein-coat gene of the
zucchini yellow mosaic virus to squash plants that had previously
sustained great damage from the virus, scientists were able to create
transgenic squash plants with immunity to this virus. Scientists
also have developed transgenic potato and strawberry plants that
are frost-resistant; potatoes, corn, tobacco, and cotton that resist
attacks by certain insect pests; and soybeans, cotton, corn, and
oilseed rape (the source of canola oil) that have increased resistance
to certain weed-killing chemicals called herbicides.
Similarly, in animal food production, the growth hormone gene of
rainbow trout has been transferred directly into carp eggs. The
resultant transgenic carp produce both carp and rainbow trout growth
hormones and grow to be one-third larger than normal carp. Other
fish that have been genetically engineered include salmon, which
have been modified for faster growth, and trout, which have been
altered so that they are more resistant to infection by a blood
virus.Recombinant DNA also has been used to clone large quantities
of the gene responsible for the cattle growth hormone bovine somatotropin
(BST) in the bacterium Escherichia coli. The hormone is then extracted
from the bacterium, purified, and injected into dairy cows, increasing
their milk production by 10 to 15 percent.
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Medicine
In 1982 the United States
Food and Drug Administration (FDA) approved for the first time the
medical use of a recombinant DNA protein, the hormone insulin, which
had been cloned in large quantities by inserting the human insulin
gene in Escherichia coli bacteria. Previously, this hormone, used
by insulin-dependent people with diabetes mellitus, had been available
only in limited quantities from hogs.
Since that time, the FDA has approved other genetically engineered
proteins for use in humans, including two cloned in hamster cell cultures:
tissue plasminogen activator (tPA), an enzyme used to dissolve blood
clots in people who have suffered heart attacks, and erythropoetin,
a hormone used to stimulate the production of red blood cells in people
with severe anemia. Another important genetically engineered drug
is interferon, a chemical that is produced by the body in tiny amounts.
Engineered interferon is used to fight viral diseases and as an anticancer
drug.
Scientists also have employed recombinant DNA techniques to produce
medically useful human proteins in animal milk. In this procedure,
the human gene responsible for the desired protein is first linked
to specific genes of the animal that are active only in its mammary
(milk-producing) glands. The egg of the animal is then injected with
the linked genes. The resulting transgenic animals will have these
linked genes in every cell of their body but will produce the human
protein only in their milk. The human protein is finally extracted
from the animal's milk for use as medicine. In this way, sheep's milk
is used to produce alpha-1-antitrypsin, an enzyme used in the treatment
of emphysema; cow's milk is used to produce lactoferrin, a protein
that combats bacterial infections; and goat's milk is used as yet
another way to produce tPA, the blood-clot-dissolving enzyme also
cloned in hamster cell cultures.
Recombinant DNA technology also is used in the production of vaccines
against disease. A vaccine contains a form of an infectious organism
that does not cause severe disease but does cause the body's immune
system to form protective antibodies against the organism. When a
person is vaccinated against a viral disease, the production of antibodies
is actually a reaction to the surface proteins of the coat of the
virus. With recombinant DNA technology, scientists have been able
to transfer the genes for some viral-coat proteins to the vaccinia,
or cowpox, virus, which was used against smallpox in the first efforts
at vaccination in the late 18th century. Vaccination with genetically
altered vaccinia is now being used against hepatitis, influenza, and
herpes simplex viruses. Genetically engineered vaccinia is considered
safer than using the disease-causing virus itself and is equally as
effective.
Gene therapy, in which a healthy gene can be directly inserted into
a person with a malfunctioning gene, is perhaps the most revolutionary
and promising of recombinant DNA technologies, but many problems remain
to be solved in getting the healthy gene into human cells. The use
of gene therapy has been approved in more than 400 clinical trials
for diseases such as cystic fibrosis, emphysema, muscular dystrophy,
and adenosine deaminase deficiency, in some instances with promising
results. However, there as yet have been no cures.
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IV. CONTROVERSIES
Public
reaction to the use of recombinant DNA in genetic engineering has
been mixed. The production of medicines through the use of genetically
altered organisms has generally been welcomed. However, critics
of recombinant DNA fear that the pathogenic, or disease-producing,
organisms used in some recombinant DNA experiments might develop
extremely infectious forms that could cause worldwide epidemics.
In an effort to prevent such an occurrence, the National Institutes
of Health (NIH) in the United States has established regulations
restricting the types of recombinant DNA experiments that can be
performed using such pathogens. In Canada, recombinant DNA products
are regulated by various government departments, including Agriculture
and Agri-Food Canada, Health Canada, Fisheries and Oceans Canada,
and Environment Canada.
Animal rights groups have argued that the production of transgenic
animals is harmful to other animals. Genetically engineered fish
raise problems if they interbreed with other fish that have not
been genetically altered. Some experts fear that this process may
change the characteristics of wild fish in unpredictable and possibly
undesirable ways. A related concern is that engineered fish may
compete with wild fish for food and replace wild fish in some areas.
The use of genetically engineered bovine somatotropin (BST) to increase
the milk yield of dairy cows is particularly controversial. Some
critics question the safety of BST for both the cows that are injected
with it and the humans who drink the resulting milk. In the United
States, a large percentage of dairy cows are treated with BST, but
in Canada, BST cannot legally be sold. Scientists at Health Canada
rejected the legalization of BST in 1999 based on evidence that
BST causes health problems for cows. In particular, the Canadian
scientists found that BST increases a cow’s likelihood of
developing mastitis, or infection of the udder, and it also makes
cows more susceptible to infertility and lameness. Nevertheless,
the scientists consider the milk obtained from cows injected with
BST to be safe for human consumption.
Transgenic plants also present controversial issues. Allergens can
be transferred from one food crop to another through genetic engineering.
In an attempt to increase the nutritional value of soybeans, a genetic
engineering firm experimentally transferred into soybean plants
a Brazil-nut gene that produces a nutritious protein. However, when
a study found that the genetically engineered soybeans caused an
allergic reaction in people sensitive to Brazil nuts, the project
was canceled.
Environmentalists fear that the transgenic plants may interbreed
with weeds, producing weeds with unwanted characteristics, such
as resistance to herbicides. An example of such interbreeding has
been demonstrated in experiments involving transgenic oilseed rape.
Environmentalists also argue that, due to natural selection, insects
quickly develop resistance to plants that have been engineered to
incorporate biological pesticides.
Opponents of genetic engineering warn that the use of genetically
modified food crops could result in unforeseen problems. They point
to a 1999 study that found that genetically modified corn produced
pollen that killed monarch butterfly caterpillars in the laboratory.
Although the study results were preliminary, as a precaution the
Environmental Protection Agency (EPA) established new regulations
in January 2000 to reduce potential risks posed by the corn crop.
Among the new rules, the EPA has asked farmers to plant unmodified
corn crops around the edges of genetically engineered corn fields
in order to create a buffer that may prevent toxic pollen from blowing
into butterfly habitats.
Many European and developing nations have voiced concern about the
health and environmental risks associated with imported genetically
modified food crops from the United States and other countries.
In early 2000, 130 nations devised the Protocol of Biosafety. Once
ratified, the treaty will require exporting nations to notify importers
when products contain genetically modified organisms, including
seeds, food crops, cattle, and fruit trees.
Some critics object to the patenting of genetically altered organisms
because it makes the organisms the property of particular companies.
For example, Costa Rica has enacted laws to prohibit the patenting
of genes of native Costa Rican species by drug companies in other
countries. To date, no laws are in place in the United States and
Canada regulating the use of cloning technology, and some people
fear the prospect of human cloning. If this technology remains unregulated,
critics fear that it will provide the ability to create an "improved"
human being with characteristics predetermined according to a scientist’s
particular bias.
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V.
DANGERS REGARDING GENETIC ENGINEERING
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, The Village Voice 1998)
· 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. (Robinson 1996)
· 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 et al 1999)
Health Hazards
· 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.
· Toxins—Genetic engineering can cause
unexpected mutations in an organism, which can create new and higher
levels of toxins in foods. (Inose 1995, Mayeno 1994)
· Allergic Reactions—Genetic engineering
can also produce unforeseen and unknown allergens in foods. (Nordlee
1996)
· 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.
· Antibiotic Resistant Bacteria—Genetic
engineers use antibiotic-resistance genes to mark genetically engineered
cells. This means that genetically engineered crops contain genes
which confer resistance to antibiotics. These genes may be picked
up by bacteria which may infect us. (New Scientist 1999)
· 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. (Mayeno 1994)
Environmental Hazards
· Increased use of Herbicides—Scientists
estimate that plants genetically engineered to be herbicide-resistant
will greatly increase the amount of herbicide use. (Benbrook 1999)
Farmers, knowing that their crops can tolerate the herbicides, will
use them more liberally.
· More Pesticides—GE crops often manufacture
their own pesticides and may be classified as pesticides by the
EPA. This strategy will put more pesticides into our food and fields
than ever before.
· Ecology may be damaged—The influence
of a genetically engineered organism on the food chain may damage
the local ecology. The new organism may compete successfully with
wild relatives, causing unforeseen changes in the environment. (Metz
1997)
· 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 irreversible.
DNA is actually not well understood. 97% of human DNA is called
³junk² because scientists do not know its function. The
workings of a single cell are so complex, no one knows the whole
of it. (San Diego Union-Tribune 2000) Yet the biotech companies
have already planted millions of acres with genetically engineered
crops, and they intend to engineer every crop in the world.
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.
