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“Herbal remedies,
used in conjunction
with modern science,
have proven to be extremely beneficial
to our four legged friends”
Jim Powell, New
Zealand vet from
“Vet’s Corner” |
Bio-tech - The Basics
What is Genetic Engineering (GE)
and what are the implications?
Genetic engineering
is the process by which genes are altered and transferred artificially
from one organism to another. Genes, which are made of DNA, contain the
instructions according to which cells produce proteins; proteins in turn
form the basis for most of a cell's functions.
Genetic engineering makes it possible to mix genetic material between
organisms that could never breed with each other. It allows people to
take genes from one species, such as a flounder, and insert them into
another species, such as a tomato - thus, for example, creating a tomato
that has some of the characteristics of a fish.
Starting in the 1980s and accelerating rapidly in the past decade, companies
have begun using genetic engineering to insert foreign genes into many
crops, including important foods such as corn and soybeans.
Just in the past few years, genetically engineered ingredients have begun
appearing in many foods in U.S. supermarkets; they have been detected
in processed foods such as infant formulas, drink mixes, and taco shells,
to name a few examples.
These foods are not labeled, so consumers have no way to know when they
are eating genetically engineered food. Genetic engineering is an extremely
powerful technology whose mechanisms are not fully understood even by
those who do the basic scientific work.
Most genetically engineered crops planted worldwide are designed either
to survive exposure to certain herbicides or to kill certain insects.
Herbicide tolerant crops accounted for 71% of the acreage planted with
genetically engineered crops in 1998 and 1999, and crops designed to kill
insects (or designed both to kill insects AND to withstand herbicides)
accounted for most of the remaining acreage. A small proportion (under
1%) of genetically engineered crops planted in 1998 and 1999 were designed
to resist infection by certain viruses.
Genetically engineered herbicide-tolerant crops are able to survive applications
of herbicides that would ordinarily kill them. The U.S. food supply currently
includes products made from genetically engineered herbicide-tolerant
crops including "Roundup Ready" canola, corn, and soybeans which are engineered
to withstand applications of Monsanto's roundup (active ingredient, glyphosate),
as well as crops engineered to survive exposure to other herbicides.
Humans have little experience with exposure to this form of the toxin.
Furthermore, in the past humans have had no opportunity or reason to ingest
any form of the Bt toxin in large quantities. When the Bt toxin is incorporated
into our common foods, we are exposed each time we eat those foods. And
of course, a pesticide engineered into every cell of a food source cannot
simply be washed off before a meal.
Toxicity can also result from characteristics introduced unintentionally.
For example, a plant that ordinarily produces high amounts of a toxin
in its leaves and low amounts in its fruit could unexpectedly begin to
concentrate the toxin in its fruit after addition of a new gene. Unpleasant
surprises of this sort can result from our ignorance about exactly how
a foreign gene has been incorporated into the engineered cell. Genetically
engineered pest-resistant (or pesticidal) crops are toxic to insects that
eat them.
For example, corn can be engineered to kill the European corn borer, an
insect in the order lepidoptera (the category that includes butterflies
and moths).
This is accomplished by adding genetic material derived from a soil bacterium,
BACILLUS THURINGIENSIS (Bt), to the genetic code of the corn. BACILLUS
THURINGIENSIS naturally produces a protein toxic to some insects, and
organic farmers sometimes spray Bt on their crops as a natural pesticide.
In genetically engineered "Bt corn," every cell of the corn plant produces
the toxin ordinarily found only in the bacterium.
Unfortunately, genetically engineered crops can have adverse effects on
human health and on ecosystems. By failing to test or regulate genetically
engineered crops adequately, the U.S. government has allowed corporations
to introduce unfamiliar substances into our food supply without any systematic
safety checks.
Here are some of the reasons why we might not want to eat genetically
engineered crops:
Ordinary, familiar foods can become allergenic through the addition of
foreign genes. Genetic engineering can introduce a known or unknown allergen
into a food that previously did not contain it. For example, a soybean
engineered to contain genes from a brazil nut was found to produce allergic
reactions in blood serum of individuals with nut allergies. Allergic reactions
to nuts can be serious and even fatal.
Researchers were able to identify the danger in this particular case because
nut allergies are common and it was possible to conduct proper tests on
blood serum from allergic individuals.
In other cases, testing for allergenic potential can be much more difficult.
When genetic engineering causes a familiar food to start producing a substance
previously not present in the human food supply, it is impossible to know
who may have an allergic reaction. Genetic engineering has the potential
to make ordinary, familiar foods become toxic.
In some cases, new characteristics introduced intentionally may create
toxicity. The Bt toxin as it appears in the bacteria that produce it naturally
is considered relatively safe for humans. In these bacteria, the toxin
exists in a "protoxin" form, which becomes dangerous to insects only after
it has been shortened, or "activated," in the insect's digestive system.
In contrast, some genetically engineered Bt crops produce the toxin in
its activated form, which previously only appeared inside the digestive
systems of certain insects.
Foreign genes can be added to cells by various methods; among other options,
they can be blasted into cells using a "gene gun," or a virus or bacterium
can be used to carry them into the target cells.
The "genetic engineer" who sets this process in motion does not actually
control where the new genes end up in the genetic code of the target organism.
The "engineer" essentially inserts the genes at a random, unknown location
in the cell's existing DNA. These newly-inserted genes may sometimes end
up in the middle of existing genetic instructions, and may disrupt those
instructions.
A foreign gene could, for example, be inserted in the middle of an existing
gene that instructs a plant to shut off production of a toxin in its fruit.
The foreign gene could disrupt the functioning of this existing gene,
causing the plant to produce abnormal levels of the toxin in its fruit.
This phenomenon is known as "insertional mutagenesis" -- unpredictable
changes resulting from the position in which a new gene is inserted.
Genetic engineering can also introduce unexpected new toxicity in food
through a well-known phenomenon known as pleiotropy, in which one gene
affects multiple characteristics of an organism.
Genetically engineered crops can indirectly promote the development of
antibiotic resistance, making it difficult or impossible to treat common
human diseases. Whatever method is used to introduce foreign genes into
a target cell, it only works some of the time, so the "genetic engineer"
needs a way to identify those cells that have successfully taken up the
foreign genes.
One way to identify these cells is to attach a gene for antibiotic resistance
to the gene intended for insertion. After attempting to introduce the
foreign genes, the engineer" can treat the mass of cells with an antibiotic.
Only those cells that have incorporated the new genes survive, because
they are now resistant to antibiotics.
From these surviving cells, a new plant is generated. Each cell of this
plant contains the newly introduced genes, including the gene for antibiotic
resistance. Once in the food chain, in some cases these genes could be
taken up by and incorporated into the genetic material of bacteria living
in human or animal digestive systems.
A 1999 study published in Applied and Environmental Microbiology
found evidence supporting the view that bacteria in the human mouth could
potentially take up antibiotic resistance genes released from food.
Antibiotic resistance among disease-causing bacteria is already a major
threat to public health; due to the excessive use of antibiotics in medical
treatment and in agriculture, we are losing the ability to treat life-threatening
diseases such as pneumonia, tuberculosis, and salmonella. By putting antibiotic
resistance genes into our food, we may be increasing the public health
problem even further.
Rachel Massey
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