What is a transgenic animal/plant?
A transgenic animal or plant is one that has a foreign gene (called
a "transgene") inserted into its DNA. Transgenic animals
and plants are sometimes called "genetically modified organisms"
or GMO's for short.
What is a transgene?
A transgene is the foreign gene that has been moved from one organism
into a new organism by genetic engineering. For example, a bacterial
gene that is inserted into a plant's DNA would be a transgene.
What is the difference between traditional
plant and animal breeding and transgenic technology?
In traditional plant or animal breeding, a plant or animal with
a desired trait is mated with an existing plant or animal, to
transfer the desired trait to the offspring. Of course, the only
genes that are involved are the genes already present in the parental
plants or animals. For example, if you mate rabbits, the only
genes that you can expect to find in the baby rabbits are rabbit
genes, which came from a rabbit egg and a rabbit sperm.
In transgenic technology, by contrast, a single gene from one organism, say a camel, could be inserted (by injection) into fertilized rabbit eggs. The camel gene would insert itself into the rabbit's DNA in some of the eggs (the success rate of this is fairly low). The rabbit eggs would then be returned to a female rabbit's womb, where the baby rabbits would develop. The eggs where a camel gene is inserted will divide and pass on the camel gene into all the cells of the developing baby rabbit, so that when it is born all of its cells now have a camel gene in them. As you can imagine, there is no "natural" way that a rabbit would mate with a camel and end up with camel genes, but with transgenic technology this is made possible. Transferring genes across species by this technology has made it possible to put human genes into goats, bacterial genes into plants and jellyfish genes into frogs.
Why would anyone want to do such bizarre things?
There are many reasons that people want to transfer genes from
one species to another.
One reason is to make pest-resistant plants. Certain bacteria produce a toxic substance that can kill insect pests that feed on crop plants. If we insert the gene for this toxin into the DNA of crop plants, then the plants would produce the toxin and any insects that attacked the plants would be killed. In this way, the plant would be able to ward off insect pests.
Another reason for putting the genes of one species into another species is to make life saving drugs in large amounts. If we insert the gene for, say, insulin, or blood-clotting factors into cows, in the right way, then we can get the cows to produce the insulin or clotting factors in their milk. Since a single dairy cow can produce upto 10,000 quarts of milk in a year, this would assure a plentiful and cheap supply of these therapeutic compounds. Remember that insulin and the clotting factors are made by humans, and we can't really use human beings as a source for these compounds, certainly not to produce the quantities that are needed.
What are genetically-modified foods?
The term GM foods is most commonly used to refer to crop plants
created for human or animal consumption using genetic engineering.
These plants have been modified in the laboratory to enhance
desired traits such as increased resistance to herbicides or improved
nutritional content.
What are some of the advantages of GM food-plants?
The world population is predicted to double in the next 50 years.
Ensuring an adequate food supply for this booming population is
going to be a major challenge in the years to come. Scientists
hope that genetically modified food plants can help in warding
off starvation as the world's population grows. The ways in which
they think that genetically modified plants can help are listed
below:
Pest resistance, described above, can help farmers to reduce their
use of chemical pesticides, which in turn can reduce the cost
of producing food.
Herbicide tolerance: Some plants have been engineered to be resistant to weed-killers, so that farmers can spray a field with the weed-killer, wiping out everything except the crop that they are interested in. Again, this reduces the cost to the farmers of growing food crops. Much of the soybean crop grown in the US is engineered to be herbicide tolerant.
Disease resistance, Cold tolerance, etc.: There are many viruses, fungi and bacteria that cause plant diseases. Plant biologists are working to create plants with genetically engineered resistance to these diseases and to cold.
Improved nutritional qualities: For millions of people in developing countries, rice is the main item in the diet. Because rice does not contain many essential nutrients, malnutrition is very common in these countries. Especially terrible is the blindness that results from a lack of vitamin A. This vitamin is abundant in milk and in vegetables such as carrots, which most of the poor people of the world cannot afford. To solve this problem, Swiss researchers created a transgenic rice variety that is high in vitamin A. They hoped that this rice, if grown and eaten in developing countries, would reduce the diseases associated with vitamin A deficiency. However, research on this rice has been halted, following protests in Europe against genetically modified foods.
What objections are raised against genetically
modified foods?
The objections to transgenic or genetically modified plants and
animals fall under three main categories:
a. Environmental concerns:
-an example of an environmental concern is whether pest-resistant
crop plants may be killing beneficial insects as well as pests.
Some studies have shown that the pollen of transgenic corn plants
is toxic to the larvae of monarch butterflies.
- another concern is whether the introduced genes will spread
from the crop plants into plants growing nearby. For instance,
if you had soybeans that were modified to be resistant to weedkiller,
people worry that weed plants growing in the fields may acquire
resistance to weedkiller by cross pollinating with the soybeans.
They are concerned that we would then have a "super weed"
that could not be killed by the weedkiller.
b. Human health concerns:
-an example: Suppose that you put a peanut gene into some other
plant (for instance broccoli) or animal (say, cows). If the transgenic
plant or animal was eaten by a person allergic to peanuts, this
might trigger a violent reaction in them. The danger of this
happening would be greater because no one would expect, say, broccoli,
or beef, to have this particular allergy-causing compound.
c. Economic concerns:
- an example: Transgenic plants are expensive to produce because
it takes fancy technology to produce them. The companies that
produce them (primarily in countries such as the US) want to make
a profit on them because they put a lot of resources into making
them. People worry that poor countries, who might benefit most
from the technology, would not be able to afford to buy the seeds.
Who regulates transgenic plants and animals?
In the US, genetically modified plants and animals are regulated
by three different agencies:
- the EPA (Environmental Protection Agency) determines if the
transgenic organism is harmful to the environment.
- the USDA (US Department of Agriculture) determines if the transgenic
plant is safe to grow as a crop.
- the FDA (Food and Drug Adminstration) determines if it is safe
to eat.
Transgenic plants have received much more attention than transgenic animals, partly because most transgenic animals are used for pharmaceutical or research purposes rather than for food. Most people don't have a problem with using animals to produce drugs for us, but they tend to mind if their food is altered in any way.
A question for you to think about:
Do you think transgenic foods should be labelled as such? If
so, why? If not, why not?
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