1. Introduction
Farmers have been using selective breeding to develop beneficial qualities in plants and
animals for traits they prefer for thousands of years. Recently a new scientific method has
been discovered that enables geneticists to transfer almost any specific trait from one
species to any other species they want. This field of research is known as genetic
modification and has only been developed in the last thirty years. The problem with the
technology is many people are not fully informed on what genetic engineering actually is
or what affects it may cause. One problem arising from this is that their ignorance does
not allow them to make an informed decision about whether or not to support or reject
genetically modified (GM) crops. This has become a controversial international issue.
This report hopes to clear up all of the misconceptions about GM crops and to enlighten
the reader about some possibilities this new technology has brought forth.
2. History of the Technology
Plant breeding started with farmers trying to breed plants that contained certain desirable
traits. The goal was to find mutations in the plants that lead to traits that would help there
crops. Then in the 1920’s different types of radiation, such as gamma rays, were used to
cause mutations within the plants. These methods along with others all helped researchers
arrive where they are now with genetically modified plants (Department of Soil and Crop
Sciences at Colorado State University, 2004).
The technology was first used in 1983 to add bacteria genes to the DNA of a plant by
three separate research groups. Later a fourth group used the technology to transfer genes
from one species of plant to another. Their discoveries were soon published in scientific
journals and these laboratory specimens lead to the creation of genetically modified
plants, also known as transgenic plants, that could be commercially valuable (Department
of Soil and Crop Sciences at Colorado State University, 2004).
3. Creation of Genetically Modified Plants
The creation of genetically modified plants, or transgenic plants, involves five main
steps. These steps are the extraction of DNA, replication of the genes of interest,
preparing the genes for integration, transformation, and breeding of the modified plants.
Figure 1 gives a visual outline of the process to be described in detail below (Pighin,
2003).
Figure 1. Overview of the Creation of Transgenic Crops (Pighin, 2003).
3.1. Identification of Genes responsible for Desired Traits
3.1.1. DNA Overview
DNA is located in each cell of a living organism and contains the genetic
information of the organism through combinations of four bases; adenine,
cytosine, guanine, and thymine. Segments of the DNA called genes hold the
information needed to synthesize proteins. These proteins would perform
functions within the cell like acting as enzymes that catalyze biochemical
reactions, being structural units, or as storage capacity within the cell. These
proteins would then derive different traits within the cells of an organism or
perhaps the whole organism. Enzymes that separate or join different segments of
DNA are used as the main tools to manipulate the DNA (Department of Soil and
Crop Sciences at Colorado State University, 2004).
3.1.2. Isolation of Genes Responsible for Desired Traits
Currently the main limiting factor involved with transgenic plants is the location
of genes responsible for the traits of interest within plants. Little is known about
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the genes responsible for desirable traits within crops and the location of these
genes is a major focus of the research into transgenic plants. However location of
the genes alone is not enough; other factors such as regulation of the gene and
how it interacts within plants must also be understood (Department of Soil and
Crop Sciences at Colorado State University, 2004; Pighin, 2003).
3.2. Replication of Gene of Interest
Once the genes that control desired traits are located they must be replicated into
large amounts before they are inserted into a plant. This is usually completed through
the use of a bacterial plasmid vector. First, the DNA that includes the genes needed is
extracted from a donor organism using a restriction enzyme. This separates the DNA
at certain locations, and a DNA segment is created. A plasmid, a small circular
section of bacterial DNA, is taken from a bacteria cell and a separation is created; this
leaves a gap in the plasmid. The DNA segment from the donor organism is stuck into
this gap in the plasmid using DNA ligase, an enzyme which sticks pieces of DNA
together, and creates a recombinant plasmid. This plasmid is placed back into the
bacteria cell where it is copied as the cell reproduces itself (Herbrandson, 2004;
Pighin, 2003).
3.3. Preparing the Gene for Integration into Plants
Once the genes have been replicated in sufficient numbers they must undergo
modifications before they can be inserted into an organism. These modifications are
needed to ensure the genes operate properly within the cells of the new plant. A
promoter must be added to the gene, this is a section of DNA that determines when
and where in the plant the genes will be expressed. A termination sequence is also
added and this indicates when the end of the gene sequence has been reached while
the cell is using the gene to produce proteins. Marker genes are also added to the
genes and they have there own promoter and termination sequences. The marker
genes indicate when a plant has successfully been transformed by allowing growth in
selective mediums. This process creates a transgene that is then inserted into the DNA
of plant cells. Figure 2 shows where the different sequences added to the gene are
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located in relation to each other with in the transgene (Department of Soil and Crop
Sciences at Colorado State University, 2004).
Figure 2. Representation of a transgene after it has been prepared for insertion into a plant.
3.4. Transformation
Once the genes have been modified accordingly, it is time to insert them into the
plants. This transformation is accomplished mainly through the two methods
discussed below. (Department of Soil and Crop Sciences at Colorado State
University, 2004; Pighin, 2003).
3.4.1. Micro-Projectile Bombardment Method
This method uses a gun firing high velocity micro-projectiles to deliver the DNA
into a cell. The DNA is stuck onto the projectiles and then they are fired into
many different types of tissues. This method supplies a clean and safe method of
transforming the plant cells and can be used on many different species of plants.
The downside involved in this method is that it can cause unwanted side effects in
the plants it is used on. (Department of Soil and Crop Sciences at Colorado State
University, 2004; Pighin, 2003).
3.4.2. Agrobacterium Method
This method makes use of Agrobacterium tumefaciens (A. tumefaciens), which is
a bacteria that infects the DNA of a plant with a piece of its own DNA. The cells
of these bacteria contain a tumor-inducing plasmid. This plasmid contains a
section of DNA that is transferred to the infected plant, transfer-DNA (T-DNA),
and is introduced into the infected plants own DNA. The plasmid also contains a
series of genes that control the infection process that takes place within the plate.
When a plant is infected, the bacteria take control of the cellular machinery in
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order to make copies of the bacterial DNA. The bacteria can only infect wounded
plants. When a plant’s stem or root is wounded, it gives off a chemical signal that
activates a response within the bacteria and begins the infection process. The
different virulence genes carry out separate steps along the infection process.
The scientific community currently uses this strain of bacteria as a natural way to
transfer DNA into a plant. The tumor-inducing section of the T-DNA is taken out
and replaced with the transgene responsible for the desired traits. A floral dip is
when the roots of a plant are dipped into a solution containing A. tumefaciens, and
is the method used to infect the seeds of a plant with the bacteria. These
transgenic seeds are then collected directly from the plant and can be used to grow
plants with the desired traits. This method allows you to transform the DNA of a
plant without jeopardizing the stability of the plant’s cell and is capable of
transferring large portions of DNA. The biggest limitation of this method is the
fact that not all crop plants can be infected with this strain of bacteria (Department
of Soil and Crop Sciences at Colorado State University, 2004; Pighin, 2003).
3.5. Breeding of Modified plants
This step involves inserting the transgenic plants into an existing population of
plants and allowing the desired trait spread through the population of plants.
(Department of Soil and Crop Sciences at Colorado State University, 2004;
Pighin, 2003).
4. Advantages and Disadvantages of Genetically Modified Crops
4.1. Advantages
4.1.1. For Farmers and Companies
Farmers have always been slaves to weather conditions and are limited to the
climatic conditions where they farm. One advantage that transgenic crops offer
farmers is the ability to grow better crops in poor conditions. This means that
once infertile land can now be made viable for agriculture. One of the first uses of
genetically modified crops was to use a gene from a cold-water flounder that
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helps the flounder survive cold water. It was inserted into a tomato so that it was
more frost resistant and experienced a longer growing season. This concept can be
applied to other applications in plant growth, such as making plants that that
survive with less water and/or sunlight, have higher tolerances for certain pests,
and perhaps in the future be resistant to animals too. Genetic engineering can also
increase yields and give crops faster maturation rates. Companies will benefit
because they are the only ones who can develop new products and they can also
put special traits into plants that give them control over the GM crops. For
example, crops with sterile seeds would require new seeds to be purchased from
the company each subsequent year (Thomashow, 1999).
4.1.2. For Consumers
Consumers always want more from the products they purchase. Genetic
engineering will yield crops with better quality attributes that will appeal to the
needs of the consumer. Geneticists can improve various traits of a plant like its
colour, size, flavour, and even the shelf-life and nutrition of the plants
(Thomashow, 1999).
4.1.3. For Developing Countries
Genetic engineering can enable poor countries to grow crops in poor conditions
thus giving them a food source that is feasible in the areas in which they live.
These advantages are similar to those for the farmer except they are applied to
whatever conditions exist in the individual developing country (Union of
Concerned Scientists, 2006).
4.1.4. For the Environment
Farmers have been polluting the earth with pesticides and herbicides for over a
century. An example of such negative affects would be how the bald eagle was
driven close to extinction from the use of DDT as a pesticide. Genetically
engineered crops provide a solution to such problems by allowing crops to be
created that produce natural pesticides to defend against pests and competitive
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plant life. A variety of corn was developed to produce its own pesticide from a
toxin that has no effects on humans but is poisonous to insects. It was originally
taken from bacteria that produced the toxin Bacillus thuringiensis, and the gene
responsible for producing the toxin was transferred to the corn plant. This can be
applied to herbicides as well (Mellon and Rissler, 2004).
4.2. Disadvantages
4.2.1. Health Risks
Since this is such a new field of discovery, some health risks involved with GM
crops are still unknown. A risk that has already been documented is allergens
resulting from proteins not normally present within the organism. The
recombination of genes will promote the growth of foreign protein sequences that
may evoke serious allergic reactions in sensitive people. Another danger is
pharmaceutical crop contamination; plants with specific medical functions not to
be used as food could cross-pollinate with food stock or seeds could simply get
mixed together so that the food products derived from it would contain potentially
harmful drugs. This is a very serious danger and stricter precautions must be taken
by the companies and farmers to prevent contamination (Mercola, 1999).
4.2.2. Environmental Risks
As with health risks, environmental risks are yet to be determined; a major risk is
the total extinction of entire species of plants. This could happen from the crosspollination of engineered foods and natural ones because of either the terminator
gene inserted by companies cause plants to become sterile, or because of the
failure of the hybrid plant to adapt to its living conditions where undesirable traits
develop in offspring. In the worst case scenario, a plant so powerful that it could
grow anywhere or cross-pollinate with anything, would wipe out entire
ecosystems simply by removing the fundamental plant that it was based upon.
The use of herbicides and pesticides could also increase due to organisms building
resistances to the modified crops (Andow et al., 2004).
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4.2.3. Economical Concerns
Traditional and organic farms will become too expensive or will become so
contaminated with foreign modified genes that it is impossible to produce food for
large markets. Farmers will be forced into using only GM crops because
conditions will be so artificial that no other plants can be grown. This will create
farmers who are controlled by corporations instead of the independent style of
farming we know today. The pioneering biotechnology firms will essentially
control all means of production for every crop being planted. From an economical
standpoint the rich will become richer and everyone will be poor (Shah, 2002).
5. Future of the Technology
The technology is in use today, but is always under development. Current research
centers on the improvement of the health of consumers. Research is currently being
carried out now to add nutritional value to plants. One example of this is vitamins being
added to crops in parts of the world where many people suffer from deficiencies. Another
path is to create plants that vaccinate or fight against diseases in the human body
(Department of Soil and Crop Sciences at Colorado State University, 2004).
6. Conclusion
This is still a young technology and is always changing and improving. The benefits
these crops could yield are almost unlimited. As discussed above the advantages of the
crops and what they can do outweigh any concrete evidence that has been found against
it. The research being carried out in this field should be continued in order to yield results
that better the world as it is today, but any new crops produced should be test thoroughly
before being released for public consumption.
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References
Andow et al. (2004) A Growing Concern: Protecting the Food Supply in an Era of
Pharmaceutical and Industrial Crops [Electronic version]. Cambridge, MA: Union of
Concerned Scientists. Retrieved November 13, from http://www.ucsusa.org/
food_and_environment/genetic_engineering/pharmaceutical-and-industrial-crops-agrowing-concern.html
Department of Soil and Crop Sciences at Colorado State University (March 2004).
Transgenic Crops: an Introduction and Resource Guide. Retrieved November 13,
2006, from http://cls.casa.colostate.edu/TransgenicCrops/index.html.
Herbrandson, Cynthia (October 2004). Chapter 14: Propagation. Retrieved November
13, 2006, from http://academic.kellogg.cc.mi.us/herbrandsonc/bio111/
propagation.htm
Mellon, M. & Rissler, J. (2004) Gone to Seed: Transgenic Contaminants in the
Traditional Seed Supply [Electronic Version]. Cambridge, MA: Union of Concerned
Scientists. Retrieved November 13, 2006, from http://www.ucsusa.org/
food_and_environment/genetic_engineering/gone-to-seed.html
Mercola, Dr. Joseph (May 1999). Health Risks of Genetically Modified Foods. The
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archive/health_risks_of_genetically_modified_foods.htm
Pighin, Jamie (2003, August). Crops: How Genetics is Providing New Ways to Envision
Agriculture. The Science Creative Quarterly. Retrieved Sept. 26, 2006, from http://
www.scq.ubc.ca/?p=518.
Shah, Anup (2002) Genetically Engineered Food. Global Issues That Effect Everyone.
Retrieved September 26, 2006, http://www.globalissues.org/EnvIssues/GEFood.asp
Thomashow, Michael F. (October 1999). Before the U.S. House Science Subcommittee on
Basic Research. Retrieved on November 14, 2006, from http://www.house.gov/
science/thomashow_100599.htm.
Union of Concerned Scientists (October 2006) Genetic Engineering. Food and
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