The most comprehensive source of GMO information on the web
Somatic embryos are embryos that originate in tissue culture in response
to plant hormones added to the growth medium. Source: National
Agricultural Biotechnology Centre, Uganda
What is a GMO?
A GMO (genetically modified organism) is the result of a laboratory
process where genes from the DNA of one species are extracted and
artificially forced into the genes of an unrelated plant or animal. The
foreign genes may come from bacteria, viruses, insects, animals or even
humans. Because this involves the transfer of genes, GMOs are also known
as “transgenic” organisms.
This process may be called either Genetic Engineering (GE) or Genetic Modification (GM); they are one and the same.
What is a gene?
Every plant and animal is made of cells, each of which has a center
called a nucleus. Inside every nucleus there are strings of DNA, half of
which is normally inherited from the mother and half from the father.
Short sequences of DNA are called genes. These genes operate in complex
networks that are finely regulated to enable the processes of living
organisms to happen in the right place and at the right time.
How is genetic engineering done?
Because living organisms have natural barriers to protect themselves
against the introduction of DNA from a different species, genetic
engineers must force the DNA from one organism into another. Their
methods include:
- Using viruses or bacteria to "infect" animal or plant cells with the new DNA.
- Coating DNA onto tiny metal pellets, and firing it with a special gun into the cells.
- Injecting the new DNA into fertilized eggs with a very fine needle.
- Using electric shocks to create holes in the membrane covering
sperm, and then forcing the new DNA into the sperm through these holes.
Is genetic engineering precise?
The technology of genetic engineering is currently very crude. It is
not possible to insert a new gene with any accuracy, and the transfer of
new genes can disrupt the finely controlled network of DNA in an
organism.
Current understanding of the way in which DNA works is extremely
limited, and any change to the DNA of an organism at any point can have
side effects that are impossible to predict or control. The new gene
could, for example, alter chemical reactions within the cell or disturb
cell functions. This could lead to instability, the creation of new
toxins or allergens, and changes in nutritional value.
But haven't growers been grafting trees, breeding animals, and hybridizing seeds for years?
Genetic engineering is completely different from traditional breeding and carries unique risks.
In traditional breeding it is possible to mate a pig with another pig
to get a new variety, but is not possible to mate a pig with a potato
or a mouse. Even when species that may seem to be closely related do
succeed in breeding, the offspring are usually infertile—a horse, for
example, can mate with a donkey, but the offspring (a mule) is sterile.
With genetic engineering, scientists can breach species barriers set
up by nature. For example, they have spliced fish genes into tomatoes.
The results are plants (or animals) with traits that would be virtually
impossible to obtain with natural processes, such as crossbreeding or
grafting.
What combinations have been tried?
It is now possible for plants to be engineered with genes taken from
bacteria, viruses, insects, animals or even humans. Scientists have
worked on some interesting combinations:
- Spider genes were inserted into goat DNA, in hopes that the goat
milk would contain spider web protein for use in bulletproof vests.
- Cow genes turned pigskins into cowhides.
- Jellyfish genes lit up pigs' noses in the dark.
- Artic fish genes gave tomatoes and strawberries tolerance to frost.
Field trials have included:
- Corn engineered with human genes (Dow)
- Sugarcane engineered with human genes (Hawaii Agriculture Research Center)
- Corn engineered with jellyfish genes (Stanford University)
- Tobacco engineered with lettuce genes (University of Hawaii)
- Rice engineered with human genes (Applied Phytologics)
- Corn engineered with hepatitis virus genes (Prodigene)
- Potatoes that glowed in the dark when they needed watering.
- Human genes were inserted into corn to produce spermicide.
Does the biotech industry hold any promise?
Genetic modification of plants is not the only biotechnology. The
study of DNA does hold promise for many potential applications,
including medicine. However, the current technology of GM foods is based
on obsolete information and theory, and is prone to dangerous side
effects. Economic interests have pushed it onto the market too soon.
Moreover, molecular marker technologies - so called Marker Assisted
Selection (MAS) used with conventional breeding - show much promise for
developing improved crop varieties, without the potentially dangerous
side effects of direct genetic modification.
Where are they?
In your food! First introduced into the food supply in the mid-1990s,
GMOs are now present in the vast majority of processed foods in the US.
While they are banned as food ingredients in Europe and elsewhere, the
FDA does not even require the labeling of GMOs in food ingredient lists.
Although there have been attempts to increase nutritional benefits or
productivity, the two main traits that have been added to date are
herbicide tolerance and the ability of the plant to produce its own
pesticide. These results have no health benefit, only economic benefit.
What foods are GM?
Currently commercialized GM crops in the U.S. include soy (94%),
cotton (90%), canola (90%), sugar beets (95%), corn (88%), Hawaiian
papaya (more than 50%), zucchini and yellow squash (over 24,000 acres).
Products derived from the above, including oils from all four, soy
protein, soy lecithin, cornstarch, corn syrup and high fructose corn
syrup among others. There are also many "invisible ingredients," derived
from GM crops that are not obviously from corn or soy. Read more
Why should you care?
Genetically
modified foods have been linked to toxic and allergic reactions, sick,
sterile, and dead livestock, and damage to virtually every organ studied
in lab animals. The effects on humans of consuming these new
combinations of proteins produced in GMOs are unknown and have not been
studied. See more under
GMO Health Risks.
Crops such as Bt cotton produce pesticides inside the plant. This
kills or deters insects, saving the farmer from having to spray
pesticides. The plants themselves are toxic, and not just to insects.
Farmers in India, who let their sheep graze on Bt cotton plants after
the harvest, saw thousands of sheep die!
Herbicide tolerance lets the farmer spray weed-killer
directly on the crop without killing it. Comparative studies on the toxic residues in foods from such crops have not yet been done.
Pollen from GM crops can contaminate nearby crops of the same type,
except for soy, which does not cross-pollinate. In fact, virtually all
heritage varieties of corn in Mexico (the origin of all corn) have been
found to have some contamination. Canola and cotton also
cross-pollinate. The long-term effects on the environment could be
disastrous. See more under
Environmental Dangers.
Genetic modification refers to techniques used
to manipulate the genetic composition of an organism by adding specific
useful genes. A gene is a sequence of DNA that contains information that
determines a particular characteristic/trait. All organisms have DNA
(genes). Genes are located in chromosomes. Genes are units of
inheritance that are passed from one generation to the next and provide
instructions for development and function of the organism. Crops that
are developed through genetic modification are referred to as
genetically modified (GM) crops, transgenic crops or genetically
engineered (GE) crops.
The main steps involved in the development of GM crops are:
-
Isolation of the gene(s) of interest: Existing
knowledge about the structure, function or location on chromosomes is
used to identify the gene(s) that is responsible for the desired trait
in an organism, for example, drought tolerance or insect resistance.
- Insertion of the gene(s) into a transfer vector:
The most commonly used gene transfer tool for plants is a circular
molecule of DNA (plasmid) from the naturally occurring soil bacterium, Agrobacterium tumefaciens.
The gene(s) of interest is inserted into the plasmid using recombinant
DNA (rDNA) techniques. For additional information see Plasmids link
- Plant transformation: The modified A. tumefaciens
cells containing the plasmid with the new gene are mixed with plant
cells or cut pieces of plants such as leaves or stems (explants). Some
of the cells take up a piece of the plasmid known as the T-DNA
(transferred-DNA). The A. tumefaciens inserts the desired genes
into one of the plant’s chromosomes to form GM (or transgenic) cells.
The other most commonly used method to transfer DNA is particle
bombardment (gene gun) where small particles coated with DNA molecules
are bombarded into the cell. For additional information see Plant
Transformation using Agrobacterium tumefaciens and Plant Transformation using Particle Bombardment links.
- Selection of the modified plant cells: After
transformation, various methods are used to differentiate between the
modified plant cells and the great majority of cells that have not
incorporated the desired genes. Most often, selectable marker genes that
confer antibiotic or herbicide resistance are used to favor growth of
the transformed cells relative to the non-transformed cells. For this
method, genes responsible for resistance are inserted into the vector
and transferred along with the gene(s) conferring desired traits to the
plant cells. When the cells are exposed to the antibiotic or herbicide,
only the transformed cells (containing and expressing the selectable
marker gene) will survive. The transformed cells are then regenerated to
form whole plants using tissue culture methods.
- Regeneration into whole plants via tissue culture
involves placing the explants (plant parts/cells) onto media containing
nutrients that induce development of the cells into various plant parts
to form whole plantlets (Figure 1). Once the plantlets are rooted they
are transferred to pots and kept under controlled environmental
conditions.
- Verification of transformation and characterization of the inserted DNA fragment.
Verification of plant transformation involves demonstrating that the
gene has been inserted and is inherited normally. Tests are done to
determine the number of copies inserted, whether the copies are intact,
and whether the insertion does not interfere with other genes to cause
unintended effects. Testing of gene expression (i.e., production of
messenger RNA and/or protein, evaluation of the trait of interest) is
done to make sure that the gene is functional.
- Testing of plant performance is generally carried
out first in the greenhouse or screenhouse to determine whether the
modified plant has the desired new trait and does not have any new
unwanted characteristics. Those that perform well are planted into the
field for further testing. In the field, the plants are first grown in
confined field trials to test whether the technology works (if the
plants express the desired traits) in the open environment. If the
technology works then the plants are tested in multi-location field
trials to establish whether the crop performs well in different
environmental conditions. If the GM crop passes all the tests, it may
then be considered for commercial production.
- Safety assessment. Food and environmental safety
assessment are carried out in conjunction with testing of plant
performance. Descriptions of safety testing are described in the Food
Safety Assessment and Environmental Safety Assessment links.
Further Reading
Figure 1: Regeneration of transgenic banana using tissue culture method
Somatic
embryos are embryos that originate in tissue culture in response to
plant hormones added to the growth medium. Source: National agricultural
Biotechnology Centre, Uganda
No comments:
Post a Comment