What exactly is a transgenic plant?
A transgenic plant is one that contains a gene or genes which have
been introduced artificially into the plant's genetic makeup using
a set of several biotechnology techniques collectively known as
recombinant DNA (rDNA) technology. DNA spliced to the coding portion
of the genes that serves to regulate how they function is also transferred
into the host plant. The inserted genes, called transgenes when
they are inserted into the new host plant, may come from another
plant of the same or a different species, or a completely unrelated
kind of organism like bacteria or animals. Bt corn varieties, for
example, contain a gene from a bacterium (Bacillus thuringiensis)
found in the soil that causes the transgenic corn to produce an
insecticidal protein. The gene being transferred may have its genetic
code altered to modify its function, in addition to having different
regulatory sequences spliced on to control how it is expressed (switched
on or off) in the plant. The process of moving genes from one species
to another is called transformation.
Once a transgenic plant is created, the transgenes can be inherited
along with the rest of the plant's genes through normal mating by
pollination. The offspring are also transgenic when they acquire
the transgenes this way. Because of this, plant breeders can take
a transgenic plant made in the laboratory and use conventional breeding
methods to develop different transgenic varieties of the crop that
are adapted for specific uses, all with the new trait provided by
the introduced genes.
Transgenic plants are often referred to as genetically engineered
(GE) plants, or genetically modified (GM) plants, although the latter
term is not preferred by some who point out that all crop plants
have been genetically modified from their original wild state by
domestication, selection and controlled breeding over long periods
of time. The U.S. Food and Drug Administration uses the term bioengineered
to describe transgenic crops. The term genetic engineering is sometimes
used more broadly to describe genetic modifications accomplished
by more conventional methods, without using recombinant DNA techniques.
For more information, see our
page on how transgenic plants are made.
Why do we want to make transgenic crops?
Very simply, the primary benefit derived from the ability to use
genes from other organisms is to increase the amount of genetic
variability available for breeders to use beyond that accessible
by conventional breeding methods.
The goal is to allow plant breeders to produce more useful and
productive crop varieties by exploiting genes from a wide range
of living sources, not just those that can be found within the crop
species itself. Progress in traditional plant breeding is limited
by the genetic diversity within each crop species, the diversity
sometimes available from closely related species, or occasionally
useful diversity created within the crop itself by inducing mutations.
Often, genes for traits that could be of benefit are not found in
a particular crop species, so the ability to make plants with new,
desirable traits borrowed from other species represents a major
technological advance over conventional breeding methods. The transgenic
crop varieties made by borrowing genes from other organisms could,
potentially, be as seemingly ordinary as tomato plants that can
produce good fruit when grown with saltier irrigation water (a trait
that might someday be added with much effort using conventional
methods) or as exotic as banana plants that produce vaccines to
protect against human illness (novel traits that would be impossible
to incorporate using traditional methods).
The methods used to make transgenic plants also allow scientists
to change crop traits by altering the crop's own genetic code, changing
the function of the products coded for by genes or changing the
way genes are expressed (switched on or off). This strategy has
been used, for example, to modify the way tomato fruits ripen to
In addition to the ability to produce crops with novel traits,
genetic engineering also offers the promise of making plant breeding
more efficient or for reducing the time required to make new varieties.
The ability to insert just one or a few specific genes into varieties
without also introducing many other genes that might negatively
affect the quality of crop varieties is often cited as a major benefit
of using technology to produce transgenic plants. Given the enormous
investment of time and money spent identifying useful genes, applying
cloning and transformation techniques, and testing and evaluating
newly transformed plants, all before conventional crossing to incorporate
the genetically engineered traits into adapted crop varieties, some
would argue that we are far from realizing this potential benefit.
Research using transgenic plants is an extremely valuable and
powerful tool to help scientists learn about how plants function.
The knowledge gained from this kind of research can be applied in
many areas of plant science, not just in the creation of new crop
varieties with novel traits.
What genetically engineered crops
are actually being grown now?
The most common genetically engineered (GE) crops now being grown
are transgenic varieties of soybean, canola, cotton, and corn. Varieties
of each of these crops have been engineered to have either herbicide
tolerance or insect resistance (or in a few cases, both).
All of the genetically engineered insect-resistant crop varieties
produced so far use specific genes taken from Bacillus thuringiensis,
a common soil bacterium, to produce proteins that are toxic to certain
groups of insects that feed on them. Currently, only Bt corn and
Bt cotton varieties are being grown in the U.S., but Bt potatoes
were on the market for several years until being discontinued in
Several different genetic modifications have been used to engineer
tolerance to herbicides, the most widely adopted GE trait overall.
Genetically engineered herbicide tolerant varieties of each of the
four major crops listed above have been developed for use with glyphosate
(Roundup®) or glufosinate (Liberty®) herbicides, and some cotton
varieties grown in the U.S. have genetically engineered tolerance
to bromoxynil or sulfonylurea herbicides. Monsanto's Roundup Ready®
soybean varieties are the most widely grown type of genetically
About half of the papaya crop produced in Hawaii is now from genetically
engineered virus-resistant varieties, but most of the world-wide
papaya crop is not genetically engineered. There is currently some
limited production of squash genetically engineered for virus resistance
in the U.S.
All together, about 50 different kinds of genetically engineered
plants (each developed from a unique "transformation event") have
been approved for commercial production in the U.S. These include
12 different crops modified to have six general kinds of traits:
||Corn, Cotton, Potato, Tomato
||Corn, Soybean, Cotton, Canola, Sugarbeet, Rice,
||Papaya, Squash, Potato
|Altered oil composition
|Delayed fruit ripening
|Male sterility and restorer system (used to facilitate
Not all of the genetically engineered varieties that have received
regulatory approval are currently being grown. Some have not yet
been marketed (herbicide tolerant sugarbeets and most kinds of GE
tomatoes, for example), and some have been commercially grown but
were later withdrawn from the market (see Discontinued
Transgenic Products). More details on the transgenic crops listed
in the table above and short descriptions of how each of the transgenic
traits works are available at http://www.comm.cornell.edu/gmo/traits/traits.html.
The AgBios GMO Database at http://www.agbios.com/dbase.php?action=ShowForm
is a useful source of information about genetically engineered crops
that have received or are undergoing regulatory approval in the
United States and other countries. You can find detailed information
on how each variety was produced, background information on why
it was done, and what concerns were addressed during the risk assessments
for environmental and food safety. Summary statistics and more information
about world-wide production of genetically engineered crops can
be found on our Current
Transgenic Products page.
Are there really economic benefits for
farmers growing transgenic crops? I've read they haven't improved
yields and cost more to plant.
Many conflicting news stories and reports have appeared concerning
the economic benefits realized by farmers adopting the major transgenic
crops. It is true that farmers pay a premium for genetically engineered
(GE) corn, soybean, and cotton varieties, and these varieties do
not have increased yield potential per se over the best available
conventional varieties. The potential economic benefits of the major
GE crops currently available could result from enhanced protection
from yield loss due to pests, increased efficiency in the production
system, or both. Actual benefits appear to vary with a number of
factors including the particular crop grown, the transgenic trait
in the crop (herbicide tolerance or Bt-derived insect resistance),
the region where the crops are grown, the type of farm operation
adopting the technology, production factors (particularly actual
pest pressures) that can vary from year to year and from farm to
farm, and the current premium paid for the transgenic seed.
Different methods used to analyze or summarize the limited data
available for these diverse situations can lead to very different
interpretations. The Economic Research Service of the USDA has issued
reports attempting to take these factors into consideration, but
their analyses do not yet include data for the most recent production
years. While particular cases may vary, some of the general conclusions
of the studies are:
While these generalizations may provide a reasonably unbiased "simple
answer" to the question, please refer to the original reports listed
below for a discussion of the factors influencing the calculated impacts,
and for an analysis of how these findings relate to the adoption of
GE crops by U.S. farmers. For example, even though the analysis showed
GE soybeans increased net returns only for some farmers, but not GE
soybean growers overall, GE soybean plantings have increased each
year from their introduction to an estimated 75% of the U.S. crop
in 2002. It has been suggested that other benefits recognized by farmers
that are more difficult to measure, such as simplified management
options, may be important in the adoption of GE-herbicide tolerant
soybeans. The AES report Adoption of Bioengineered Crops is available
and Genetically Engineered Crops: U.S. Adoption and Impacts is available
- GE herbicide-tolerant cotton and GE herbicide-tolerant corn
both have had positive economic impacts on farms overall.
- GE herbicide-tolerant soybeans have not had a positive economic
impact overall, but adoption was "quite" profitable for some farms.
Bt cotton had a positive economic impact on farms overall.
Bt corn had a negative economic impact on farms overall.
Has there actually been a reduction
in pesticide use resulting from planting transgenic crops? I understand
this is supposed to be one of the major benefits of these GE crops.
The potential for reduction in pesticide use or the substitution
of less environmentally hazardous pesticides for those currently
used on conventional crops has been proposed as a benefit of certain
genetically engineered (GE) crops. This was certainly the case for
genetically engineered corn and cotton varieties incorporating Bt
genes for resistance to certain classes of insects, where the insecticidal
compounds produced by the plants were expected to negate the need
for additional insecticide applications to control the targeted
pests. GE herbicide-tolerant crops are designed to be used with
specific herbicides, so reductions in pesticide use might be realized
if switching to a new herbicide application program compatible with
a particular GE crop requires less pesticide than the pesticide
applications it replaces. Unfortunately, it is difficult to directly
compare the impact of these substitutions because application rates,
as well as toxicity and environmental hazards, vary for different
herbicides. Pesticide use patterns also change for reasons unrelated
to the switch to GE crops, and this can complicate comparisons made
Several studies have used data collected by the USDA or industry
sources to compare the amount of insecticides or herbicides applied
to GE crops compared to conventional crops. Different ways of expressing
pesticide use (see Fun with Pesticide Numbers at http://www.comm.cornell.edu/gmo/issues/pestnum.html
for a simple example) and grouping data have resulted in different
conclusions. An aspect that is obscure in most analyses is the correlation
of effects on production with actual changes in the amount or type
of pesticides applied. For example, changing pesticide applications
can affect yields based on the effectiveness of pest control, but
yield changes could also be due to some other production factor.
Although not indisputable, several studies have offered these
References and additional resources:
- A USDA-ERS econometric model that attempts to control for other
variables suggests that, overall, a reduction in pesticide use
in the U.S. was associated with the adoption of GE insecticide
resistant and herbicide tolerant crops.
- Most comparisons of insecticide use have shown small or not
statistically significant reductions attributable to use of Bt
corn compared to conventional corn varieties overall. Reasons
for this may be because many U.S. Corn Belt corn acres are not
actually sprayed specifically for European corn borer (the primary
pest targeted by current Bt corn varieties), since outbreaks of
this pest are difficult to control and are extremely variable.
Also, insecticides used against the European corn borer are also
used to control other insect pests and generally would still be
applied independently of European corn borer pressure. Some studies
have attributed regional increases in yield to better control
of European corn borer in Bt corn. In cases where this is true,
although the total amount of pesticides released into the environment
may not decrease, yield per unit of pesticide applied may increase.
(Note that these estimates do not count the Bt toxin produced
by the plants as a pesticide application.)
- When considering insecticides directed at pests targeted by
Bt cotton (cotton bollworm, tobacco budworm, and pink bollworm),
both the number of insecticide applications and the pounds of
insecticide used on cotton were significantly lower in 1998 and
1999 in six cotton growing states compared to applications in
1995, prior to the introduction of Bt cotton. These reductions
are substantial, representing about 10-14% of the total amount
of pesticides used in those states. It is unclear precisely how
much of this reduction is directly attributable to the use of
Bt cotton. Reductions of insecticide applications (acre-treatments,
adjusted for changes in acreage planted) for Bt-targeted pests
and significant decreases in yield loss due to Bt-targeted pests
were reported in twelve of sixteen cotton producing states in
the U.S. in 1998 and 1999 compared to 1995.
- Herbicide applications to soybeans, quantified as total pounds
of herbicide active ingredient applied, have increased slightly
overall with the adoption of herbicide-tolerant GE varieties,
largely because the increased number of pounds of glyphosate applied
to Roundup-Ready® soybeans (the most widely adopted type of GE
crop in the U.S.) exceeded the reduction in the number of pounds
of other herbicides replaced by glyphosate. It has been proposed
that the substitution of glyphosate for other herbicides is environmentally
beneficial since glyphosate has lower toxicity to mammals, fish,
and birds, is less likely to leach, and is less persistent in
the environment than the herbicides it replaces.
Agricultural Biotechnology: Updated Benefit Estimates, sponsored by
the National Center for Food and Agricultural Policy; available at
Genetically Engineered Crops: U.S. Adoption and Impacts; available
Genetically Engineered Crops: Has Adoption Reduced Pesticide Use?;
available at http://www.ers.usda.gov/publications/agoutlook/aug2000/ao273f.pdf
Genetically Engineered Crops for Pest Management in U.S. Agriculture;
available at http://www.ers.usda.gov/publications/aer786/
Additional discussion of this issue, including more references, is
available in our discussion
of the potential for reducing herbicide applications.
What are the chances I'm eating food
made from genetically engineered crops?
Depending on what you eat, the chances could be fairly high
that you are eating some genetically engineered (GE) food. About
twelve different kinds of GE food crops have been developed for
commercialization, but only six of these are currently being grown
(corn, soybeans, canola, cotton, squash, and papaya) and have some
chance of being part of the food you eat. Even though there are
only a few different kinds of GE crops now being grown, it has been
estimated that as much as 60 to 70% of the food now in the U.S.
marketplace may contain at least a small amount of some ingredient
derived from a genetically engineered crop, most commonly corn or
soybeans. Since there are no genetically engineered varieties of
most kinds of food crops in production, you can be sure those whole
foods are not genetically engineered. But knowing exactly which
processed foods may have some GE ingredient, or knowing what percentage
of those foods might have come from a GE crop is usually difficult.
How do the few kinds of GE crops end
up in such a high percentage of our food?
Almost all of the genetically engineered content in food currently
comes from just four major crops: soybeans, corn, canola, and cotton
(as cottonseed oil). But products made from these major crops are
used as ingredients in a wide array of processed food. Just a few
examples include such common corn-based ingredients as corn starch,
corn flour, masa, corn syrup, corn oil, sweeteners, and certain
vitamins. Common soy-based ingredients include soybean oil, flour,
lecithin, protein extracts, and Vitamin E. Similarly, canola and
cottonseed oils are used in many products including salad dressings,
margarines, processed cheese, "non-dairy" products, potato and corn
chips, cookies, and pastries.
Since GE and conventional varieties of these crops are not usually
kept separate as they move from the farm to the processor, foods
made with ingredients derived from these four major crops may have
some GE content. Many of the ingredients derived from these crops
are so highly processed or refined that it could be difficult to
determine whether they came from GE, non-GE, or mixtures of both
kinds of crops.
Certified organic food is handled differently. To be sold as "organic",
detailed record-keeping during all phases of production and processing
is required to assure crops or ingredients made from them are not
mixed with non-organically grown or GE food. The Cooperative Extension
Service at Cornell University (Genetically Engineered Organisms
-- Public Issues Education Project) has developed an informative
discussion of how likely you are to encounter GE food in today's
market based on which genetically engineered crops have been approved
for production in the U.S. For more information, visit GE Foods
in the Market at http://www.comm.cornell.edu/gmo/crops/eating.html.
Can I avoid GE food if I buy only organically
Yes, if you buy food labeled "100% organic", "organic" (95% or more
organic content) or "made with organic [food or food group]" (70-95%
organic content) you have some assurance the food has not been genetically
engineered. By law, foods with these label designations (which appear
on the product label's principal display panel) cannot be genetically
engineered single foods or contain genetically engineered ingredients,
including the non-organic ingredients. Foods with a total content
of less than 70% organic ingredients may have the organic components
identified specifically in the list of ingredients, but the non-organic
components are not required to be free of genetically engineered
products. Food in this last category cannot have the word "organic"
on the principal display panel of the label.
Labeling requirements for food sold as organic in the U.S. are
defined in the final rules for the National Organic Program, which
operates under the direction of the Agricultural Marketing Service
of the USDA. The program was authorized by the Organic Foods Production
Act of 1990. The list of "excluded methods" pertaining to genetically
modified organisms includes "cell fusion, microencapsulation and
macroencapsulation, and recombinant DNA technology (including gene
deletion, gene doubling, introducing a foreign gene, and changing
the positions of genes when achieved by recombinant DNA technology)."
The excluded methods do not include "the use of traditional breeding,
conjugation, fermentation, hybridization, in vitro fertilization,
or tissue culture."
One concern that some people opposed to genetically engineered
foods have expressed about the rules for the National Organic Program
is that they do not specifically address issues that could arise
from inadvertent cross-pollination of organically grown crops by
genetically engineered crops.
For more information on labeling organic food, see the National
Organic Program's labeling fact sheet. Complete information about
the National Organic Program is available at http://www.ams.usda.gov/nop/.
Why do organic farming advocates object
to transgenic crops using Bt genes while accepting the use of Bt
sprays as an acceptable insect control measure?
Bt (Bacillus thuringiensis) is a naturally occurring soil
bacterium that produces proteins (called Cry proteins) toxic to
certain insects. Various kinds of the insecticidal Cry proteins,
with effectiveness against different groups of insects, are produced
by different strains of Bt. Spray formulations of Bt have been used
as insecticides for over forty years, and recently the genes that
encode certain Bt Cry proteins have been cloned and used to genetically
engineer several crop species to produce insect resistant varieties.
A major concern of many people, not just organic growers, is that
widespread use of Bt genes in genetically engineered crops will
increase the likelihood that pest populations will develop resistance
to the Bt toxins. If this occurs, not only will the utility of Bt
crops be diminished, but farmers who currently rely on Bt foliar
pesticide applications could suffer important losses as well. At
least one case where an insect (the diamondback moth) has developed
resistance to Bt in response to heavy use of spray applications
in an agricultural environment has been documented, and the development
of resistance to Bt by several species of insects has been demonstrated
in the laboratory. Most scientists agree that the development of
resistant insect populations is a potential hazard associated with
the use of genetically engineered Bt crops. There is a concern that
genetically engineered Bt crops may pose a higher risk for insects
developing resistance than that posed by conventional spray applications
because they place a very high selection pressure on the pests,
and they currently lack additional insecticidal components or synergistic
compounds found in Bt spores that might act to prevent or delay
development of resistance.
In response to these concerns, the EPA has imposed several requirements
for developing and implementing resistance management strategies,
and for monitoring insect populations for resistance. Provisions
for remedial actions, such as prohibiting Bt crops in certain areas
based on the results of pest monitoring, are part of these regulations.
A major component of the resistance management strategy is a requirement
for planting refuge areas of specified size to non-Bt varieties
along with Bt crop varieties. The purpose of the refuge is to maintain
an adequate breeding population of susceptible insects to intermate
with insects that might carry a mutation for resistance, hopefully
keeping the frequency of the resistance alleles low in the insect
populations. Companies marketing Bt crop seed are required to inform
growers about the proper methods of integrating non-Bt refuge areas
with Bt crops, and growers must sign contracts agreeing to comply
with resistance management practices. The companies also are required
to monitor the development of insect resistance, provide annual
reports on the efficacy of resistance management plans, and implement
remedial action plans in the event that resistance is detected among
pest populations. There is an ongoing debate over the requirements
for effective refuge designs, and there is some concern about how
well the refuge strategy will work. Additional strategies to avoid
resistance, such as including more than one Cry gene in crop varieties,
are being developed.
More details about refuge requirements and resistance management
strategies can be found at the following links:
How do we know genetically engineered crops
are safe to eat?
The primary concern many people have about genetically engineered
(GE) crops is the safety of food made from them. Although there
continues to be quite a bit of controversy over this issue, no evidence
has been found that foods made with the genetically engineered crops
now on the market are any less safe to eat than foods made with
the same kinds of conventional crops. Genetically engineered crop
varieties are being subjected to far greater scientific scrutiny
than that ordinarily given to conventional varieties, even though
many scientists have argued that there is no strict distinction
between the food safety risks posed by genetically engineered plants
and those developed using conventional breeding practices.
Safety assessments of foods developed using genetic engineering
include the following considerations:
evaluation of the methods used to develop the crop, including
the molecular biological data which characterizes the genetic change
the evaluation for the expected phenotype
the general chemical composition of the novel food compared to
the nutritional content compared to conventional counterparts
the potential for introducing new toxins
the potential for causing allergic reactions.
The goal is not to establish an absolute level of safety, but rather
the relative safety of the new product so that there is a reasonable
certainty that no harm will result from intended uses under the
anticipated conditions of production, processing and consumption.
Since conventional crops have known histories of safe use given
certain identifiable risk factors, genetically engineered crops
are considered to have the same relative safety as their conventional
counterparts if they do not differ significantly from conventional
crops for these risk factors. See http://www.agbios.com/cstudies.php?book=FSA&ev=MON810&chapter=Preface
for examples of the food safety assessment for two genetically engineered
Some critics of GE crops point out that a lack of evidence for
harmful effects does not mean they do not exist, but just as likely
could mean that we have not done the proper studies to document
them. Some reject the idea that we face the same kinds of risks
from GE crops as from conventionally developed crops, believing
the genetic engineering process itself introduces unique risks.
A major concern often expressed about GE food safety is the risk
for unintentional, potentially harmful changes that may escape detection
in the evaluation process. It is true that the number of factors
that are examined for change is small compared to the total number
of components produced by plants. Also, more extensive comparisons
of plant chemical compositions would be difficult because complete
data describing the composition of conventional crop plants, including
knowledge of variability among different cultivars or that due to
environmental influences, is lacking. The random nature of transgene
insertion when making GE plants, it is argued, may cause disruption
of important genes, causing significant effects but little obvious
change to the plant's phenotype. Additional opinions and considerations
about the safety of genetically engineered foods can be found in
of risks to human health and at http://www.comm.cornell.edu/gmo/issues/issues.html
Why is there so much debate about mandatory
labeling of genetically engineered foods?
Whether or not to require mandatory labeling of genetically engineered
(GE) foods is a major issue in the debate over the risks and benefits
of food crops produced using biotechnology. The issue is complex
because (1) many arguments put forth in the debate are based on
disagreements about the adequacy of our scientific understanding
of the consequences of genetic engineering; and (2) significant
changes to our current food marketing and manufacturing system,
with potentially large economic impacts, would be required to implement
Central to the arguments for mandatory labeling is that consumers
have a right to know what is in their food. This is especially true
for some products made with biotechnology where health and environmental
concerns have not been satisfactorily resolved. Some people do not
wish to use genetically engineered products for religious or ethical
reasons. Labeling is the only way consumers can make informed choices,
whatever their reasons may be.
Major arguments against mandatory labeling have addressed the
practical concerns about the expense and complex logistics that
would be required to ensure GE and conventional foods are kept separate
or to test all foods for GE content. It is argued that such measures
are unnecessary since no significant differences have been found
between today's GE foods and conventional foods.
Enacting mandatory labeling will also require resolving certain
other questions. Major issues include defining exactly what kinds
of technologies would be covered, deciding on tolerance levels for
genetically engineered content or ingredients before labeling would
be required, and choosing a method for verifying that products are
properly labeled. Please see the fact sheet Labeling
of Genetically Engineered Foods for a full discussion of the
arguments for and against mandatory labeling and the issues that
will have to be resolved if such legislation is enacted.
Aren't there some food labeling requirements
for genetically engineered foods now?
Under current policy, the U.S. Food and Drug Administration does
not automatically require all genetically engineered food to be
labeled. Conventional and genetically engineered (GE) foods are
all subject to the same labeling requirements, and both may require
special labeling if particular food products have some property
that is significantly different than what consumers might reasonably
expect to find in that kind of food. Therefore, particular genetically
engineered foods are subject to special labeling requirements if
the FDA concludes they have significantly different properties including:
- a different nutritional property from the same kind of conventional
a new allergen consumers would not expect to be in that kind of
food (a hypothetical example would be an allergenic peanut protein
in GE corn or some other crop)
- a toxicant in excess of acceptable limits.
Examples of genetically engineered foods that require special labeling
are those that contain vegetable oil made from varieties of GE soybeans
and canola where the fatty acid composition of the oils extracted
from the seeds of these crops was altered. Since the oils from these
varieties have different nutritional properties than conventional
soy and canola oils, foods made with them must be labeled to clearly
indicate how they are different. You might see "high laurate canola"
or "high oleic soybean" on food labels if these products were used.
The FDA does not require them to be labeled as "genetically engineered",
but that information could also be included on the label.
So far, no approved, commercially grown genetically engineered
food crops have known properties that would require foods made from
them to be labeled because they contain a new allergen or excess
levels of toxic substances.
The FDA has recently proposed voluntary guidelines for labeling
food that does or does not contain genetically engineered ingredients
to help industry provide information to consumers in a manner the
FDA considers to be accurate and not misleading in accordance with
established food labeling policy. Federal legislation has been proposed
that would require mandatory labeling of genetically engineered
foods, and similar initiatives at the state or local level have
been considered or are currently pending. For more information,
see the fact sheet Labeling
of Genetically Engineered Foods.
Haven't people had allergic reactions
from eating transgenic corn and soybeans?
Some people are allergic to proteins that occur naturally in soybeans,
and they could have a reaction if they are exposed to either conventional
or transgenic soybeans or soy products. Soybeans are one of the
eight most common sources of food allergies. Although less common,
some people have food allergies associated with corn and they could
be affected by either conventional or transgenic corn. No allergic
reactions attributable to the proteins present as a result of genetic
engineering have been reported in the transgenic soybeans being
grown commercially at this time. Reports of an allergenic protein
made as a result of genetic engineering in one particular type of
transgenic corn could not be confirmed by subsequent testing.
While there isn't any evidence that allergens have been introduced
into food crops by genetic engineering, two incidents have received
quite a bit of publicity and caused public concern about food allergies
resulting from transgenic crops.
The first incident involved soybean plants being developed by
Pioneer Hi-Bred in the early 1990's. Pioneer used a gene from Brazil
nuts to make soybeans that contained higher levels of the amino
acid methionine. They wanted to make a more nutritious chicken feed
that would eliminate the need for expensive feed supplements. While
these transgenic soybeans were being tested, research funded by
Pioneer discovered that the protein made by the Brazil nut gene
could cause allergic reactions in humans. Pioneer stopped development
of these soybeans in 1993, and they were never sold or grown for
market. You can find Pioneer's account of this story at http://www.pioneer.com/biotech/brazil_nut/default.htm.
The second incident involved reports of allergic reactions in people
who may have eaten food containing the insecticidal protein called
Cry9C, one of several forms of the Bt insecticide. The gene for
this protein had been genetically engineered into Starlink corn
by Aventis CropScience. Starlink corn had only been approved for
use as animal feed or for industrial purposes, but not for human
consumption, because tests made when Starlink was being developed
showed the Cry9C protein had certain characteristics in common with
other proteins known to be allergenic. When food from grocery shelves
tested positive for Cry9C, demonstrating that Starlink had accidentally
made its way into the food supply, a massive screening and recall
effort was put into effect. During this time, the reports surfaced
of allergic reactions in people who had eaten corn products that
may have been contaminated by Cry9C. The Food and Drug Administration
and Centers for Disease Control investigations that followed found
28 cases where people had apparently suffered allergic reactions
to something, but the special test developed by the FDA (an enzyme-linked
immunosorbent assay, or ELISA test, to detect people's antibodies
to the Cry9C protein) did not find any evidence that the reactions
in the affected people were associated with hypersensitivity to
the Cry9C protein. The test isn't 100% conclusive, though, partly
because food allergies may sometimes occur without detectable levels
of antibodies to allergens. The EPA ruled on July 27, 2001, to keep
a zero tolerance policy for Cry9C in food, based on the original
suspicions of potential allergenicity. You can review the CDC report
More information about the Starlink corn incident can be found in
on StarLink corn. A more detailed discussion of concerns about
food allergies resulting from transgenic crops is available in our
discussion of allergies.
How does the government regulate genetically
The federal government first adopted a "Coordinated Framework for
Regulation of Biotechnology" in 1986. Under this system, three federal
agencies have regulatory authority over genetically engineered (GE)
crops. Each agency has a different role to ensure safety under specific
legislation. These agencies and their regulatory responsibilities
- The U.S. Department of Agriculture (USDA), through the Animal
and Plant Health Inspection Service (APHIS), is responsible for
assuring that any organism, including genetically engineered organisms,
will not become pests that can cause harm if they are released
into the environment. APHIS has used their authority to grant
permission and set the rules for field testing of genetically
engineered crops. These crops cannot be commercialized until they
are granted "non-regulated" status by APHIS upon satisfactory
review of the field testing data. Detailed information about the
procedures APHIS uses to regulate genetically engineered plants
is available at http://www.aphis.usda.gov/ppq/biotech/.
- The Food and Drug Administration (FDA) is responsible for ensuring
the safety of most food (except for meat, poultry and some egg
products, which are regulated by the U.S. Department of Agriculture),
including food from genetically engineered crops. If the allergen,
nutrient and toxin content of new GE foods fall within the normal
range found in the same kind of conventional food, the FDA does
not regulate the GE food any differently. So far, all genetically
modified foods in the U.S. marketplace have gone through a voluntary
review process where the FDA determines whether they are "not
substantially different" from the same conventional foods by consulting
with developers of new GE foods to identify potential sources
of differences, then reviewing a formal summary of data provided
by the developer. Recently, the FDA has announced a new rule that
would make pre-market consultation mandatory. The FDA has the
authority to order foods to be pulled from the market at any time
if are found to be unsafe, or to require labeling of any food
that has different amounts of allergens, nutrients, or toxins
than a consumer would expect to find in that kind of food. Information
from the FDA about their role in regulating GE foods is available
- The Environmental Protection Agency (EPA) evaluates the safety
of any pesticides that are produced by genetically engineered
plants. The EPA calls novel DNA and proteins genetically engineered
into plants to protect them against pests "plant incorporated
protectants" (PIPs) and regulates them the same way they regulate
other pesticides. EPA documents concerning plant incorporated
protectants can be found at http://www.epa.gov/pesticides/biopesticides/.
Under the Coordinated Framework, some kinds of genetically engineered
crops might not be subject to the oversight of all three agencies.
For example, an ornamental flower like petunias engineered to have
longer lasting blooms may only have to meet the requirements of
APHIS, but a food crop like soybeans engineered to produce an insecticidal
compound would be subject to the rules of all three agencies. Additional
regulations are imposed by some states, but Colorado does not currently
have additional requirements. Also, the National Institutes of Health
has developed safety procedures for research with recombinant DNA.
Most institutions developing genetically engineered crops follow
the NIH guidelines, and they are required for federally funded research.
A useful overview of the U.S. regulatory process, including links
to information about the laws granting authority to the agencies
and their primary rules and regulations, is available at http://www.aphis.usda.gov/ppq/biotech/usregs.html.
The regulatory process is complex and changes are being proposed
by the regulatory agencies themselves, independent scientific review
panels, and the public. Detailed discussions of how the regulatory
system works and some issues raised by critics of the current system
can be found in the following links:
our page on evaluation and regulation of crops at /TransgenicCrops/evaluation.html,
Cornell University's page at http://www.comm.cornell.edu/gmo/regulation/reg.html,
and the AgBios web site at http://126.96.36.199/agbios/regulate.php?action=USA
How is "substantial equivalence" used
to determine the safety of genetically engineered food?
The principle of substantial equivalence is a functional part of
the current risk assessment process used to evaluate the safety
of new foods produced using biotechnology. Basically, the concept
of substantial equivalence is that novel crops or foods, such as
those made using genetic engineering, can be compared with the same
kinds of conventional crops or foods that have established histories
of safe use given certain known risk factors.
A number of properties of the novel and conventional products,
including the levels of nutrients, toxic substances, and potential
allergens, may be compared taking into account established patterns
of processing and consumption. If the comparison reveals that there
are no significant differences between the two kinds of food, the
novel food is presumed to be no less safe than the conventional
Substantial equivalence is not an evaluation of the absolute safety
of a novel biotech product, but rather a practical method to establish
food safety relative to an analogous conventional product with familiar
levels of safety and risks. In practice, if the Food and Drug Administration
finds that bioengineered foods are "not substantially different"
from conventional foods, they are not regulated any differently
and are considered interchangeable with the conventional foods for
use in the U.S. Where a product is found not to be substantially
equivalent to an existing one, further investigations focusing on
the identified differences would be required to establish risk factors.
Lack of substantial equivalence does not necessarily mean the
novel product isn't safe. For example, soybeans genetically engineered
to produce oil with a different fatty acid composition (an identified
nutritional difference) from conventional soybeans might have an
advantage over conventional soybean oil when used for cooking because
the GE soybean oil eliminates the need for industrial hydrogenation,
which produces undesirable trans-fatty acids. Totally new foods,
where no similar materials have ever been consumed, could not be
evaluated using substantial equivalence and would have to be evaluated
solely on the basis of their own unique properties.
Critics of our current evaluation process argue that comparing
genetically modified and conventional foods for differences in a
few known risk factors is not adequate evidence that they are safe
for human consumption. Concerns center on possible unexpected effects
that may escape study and that substantial equivalence has never
been properly defined or cannot really be fully tested.
A more detailed discussion of how substantial equivalence is used
to evaluate novel food safety and what some of the major limitations
are is available at http://www.agbios.com/cstudies.php?book=FSA&ev=MON810&chapter=Concepts.
A recent scientific review published by The Royal Society of the
United Kingdom also contains a detailed critique of substantial
equivalence. This report can be found at http://www.royalsoc.ac.uk/files/statfiles/document-165.pdf.
Why do GE plants have antibiotic resistance
genes? Doesn't this pose a risk for developing resistant strains
Antibiotic resistance genes are frequently used at several stages
in the creation of genetically engineered plants as convenient "selectable
markers". Bacteria or plant cells without a gene for resistance
to the antibiotics used can be killed when the antibiotic is applied
to them. So when scientists link the gene for the desired trait
being introduced into a plant with an antibiotic resistance gene,
they can separate cells carrying the desired gene from those that
don't by exposing them to the antibiotic. The antibiotic resistance
genes end up in the genetically engineered plants as excess baggage
whose function is no longer required after the process of making
them is complete.
Concern has been raised about the possibility that antibiotic
resistance genes used to make transgenic plants could be transferred
to microorganisms that inhabit the digestive tracts of humans or
other animals that eat them, and therefore might contribute to the
already serious problem of antibiotic resistant pathogens. Transfer
of DNA from one microbe to another (horizontal gene transfer) is
known to occur in nature and has been observed in some laboratory
experiments under specific conditions, but the likelihood of DNA
being transferred from plant material in the digestive system to
microbes has not yet been experimentally determined. It is thought
that for such a transfer to be possible, it would have to come from
consumption of fresh food since most processing would degrade the
plant's DNA. Also, there is evidence that most DNA is rapidly degraded
by the digestive system. However, results of one recent experiment
have suggested that horizontal transfer of DNA from genetically
engineered plants can occur in the human digestive tract under some
circumstances. But overall, the risk of antibiotic resistance genes
from transgenic plants ending up in microorganisms appears to be
A second concern about the use of some antibiotic resistance genes
is that they could reduce the effectiveness of antibiotics taken
at the same time transgenic food carrying the resistance gene for
that antibiotic was consumed. In cases where this has been identified
as a risk based on the mechanism of resistance, studies have suggested
the chance of this happening was probably very low due to rapid
digestion of the inactivating enzymes produced by the transgenic
resistance gene. Most transgenic plants do not carry resistance
genes for antibiotics commonly used to treat infections in humans.
While the risk of creating additional problems of antibiotic resistance
in microorganisms from the use of the resistance genes in transgenic
plants appears to be low, steps are being taken to reduce the risk
and to phase out their use. The FDA recommends that developers of
transgenic crops use only antibiotics that are not commonly used
for treatment of diseases in humans. Scientists are developing and
using different selectable markers, and are also experimenting with
methods for removing the antibiotic resistance genes before the
plants are released for commercial use. Further discussion of concerns
about the use of antibiotic resistance genes in genetically engineered
plants can be found in our
discussion of antibiotic resistance genes and in a report by
the Royal Society at http://www.royalsoc.ac.uk/files/statfiles/document-56.pdf
Are there health risks from eating the
foreign DNA in transgenic plants?
It is unlikely that eating DNA poses any significant risk to human
or animal health, and there is no evidence to suggest that there
is any additional risk from the transgenes present in genetically
Normal diets for humans and other animals contain large amounts
of DNA. This DNA comes not only from the cells of the various kinds
of plants or animals constituting the food, but also from any contaminating
microorganisms or viruses that may be present in or on the food.
We have been exposed to this variety of DNA throughout our entire
Most of the DNA we eat is degraded in the digestive system, but
some experiments have shown that small amounts of it can be found
in some cells in the body. It is thought to be unlikely that this
DNA would be incorporated into the DNA of those cells, but even
if it was, the chance of any undesirable effect on the whole organism
is thought to be very low.
There is evidence to suggest that certain kinds of intact genetic
elements have been incorporated into human DNA sometime during our
history, but there is a lack of recognized negative consequences
to our health that can be attributed to this. It seems that we are
well adapted to handling exposure to DNA, and there is no obvious
reason that the DNA from other organisms introduced into crops by
genetic engineering would have any additional effect. References
for research in this area and further discussion can be at found
in our discussion of
eating DNA or in a longer review of risks posed genetically
engineered crops published by The Royal Society of the United Kingdom.
The report is available at http://www.royalsoc.ac.uk/files/statfiles/document-56.pdf.
I hear the terms "genetic drift" and
"genetic trespass" in the debate about transgenic crops. What do
"Genetic drift" or "pollen drift" used in this context refers to
the unintentional transfer of pollen from transgenic crops to nearby
conventional crops by wind or insects. Seeds produced on the conventional
crop resulting from pollination by the transgenic crop will also
contain the genes of the transgenic crop. The term is meant to describe
problems with contamination of non-genetically engineered crops
by transgenes in the same way "pesticide drift" is used to describe
contamination of non-target crops by errant pesticide applications.
You might also see the phrase "crop-to-crop gene flow" used to describe
the transfer of genes from one crop variety to another by cross-pollination.
"Genetic drift" has a different meaning in the field of population
Seed producers have long been concerned with preventing cross-pollination
among crop varieties in order to maintain the purity (the genetic
identity) of each of the varieties they grow. The chance of pollen
drift from transgenic crops has raised additional issues about the
purity or "identity" of crops entering the marketplace. For example,
crops grown for the organic market cannot be genetically engineered.
What happens if they are partially cross-pollinated by a genetically
engineered crop? Can they be sold as organic? What tolerance levels,
if any, should be established to account for small amounts of cross-pollination?
Who is responsible for preventing cross-pollination? Is a grower
guilty of "genetic trespass" if pollen from his crop affects the
marketability of a neighbor's crop? Producers of conventionally
grown crops for export are also facing these issues because some
markets have banned genetically engineered food.
Pollen drift is more likely with naturally cross-pollinating crops
like corn than with highly self-pollinating crops like soybeans.
Problems can be prevented by carefully maintaining crop-specific
isolation distances between different varieties. Sometimes additional
strategies are employed, such as using border strips around fields
to trap pollen. More information about the concerns arising from
the potential for "genetic trespass" is available in our
discussion of crop-to-crop gene flow.
I'm concerned by the reports of transgenic
DNA found in Mexican corn landraces. Isn't this evidence that transgenic
crops will cause environmental damage by reducing genetic diversity?
Genes engineered into crops can be transmitted to other plants of
the same species or to sexually compatible wild relatives by pollination.
Hybridization of transgenic crops with other plants raises environmental
concerns on several fronts, including the possible introduction
of traits that could increase the weediness of some species, the
potential for affecting the genetic diversity or ecological status
of natural, non-weedy plant populations, and the potential for affecting
the genetic diversity found in crop landraces (traditional, locally
adapted varieties). Of course, gene flow from conventional, non-genetically
engineered crops also occurs, and has been implicated in causing
undesirable changes in certain natural plant populations and in
the evolution of more aggressive weeds for several crops. Many factors
influence the potential consequences of gene flow from crops, and
whether transgenic crops are more or less likely to cause undesirable
effects is unknown.
The recent reports of transgenic DNA in corn growing in southern
Mexico, despite a government moratorium since 1998 on planting transgenic
corn, generated a great deal of concern, since this region is a
center of genetic diversity for maize (corn) and the potential effects
of transgenes introduced from genetically engineered varieties on
the landraces or wild maize relatives growing there are unknown.
While the study reporting the presence of transgenic DNA in Mexico
has generated controversy over the methodology used and certain
conclusions, the plausibility of transgenic corn growing in Mexico
is generally not questioned. Continued monitoring and additional
research, however, will be needed to understand the actual effect
on genetic diversity, if any, of introducing a few, specific genes
into the maize populations of Mexico. Concerns about the difficulty
of controlling the spread of transgenes via crop-to-crop or crop-to-wild
gene flow are valid. Examples from existing population genetics
research suggest there will not be a universal answer to describe
the risks of gene flow from any particular transgenic crop. Each
kind of transgenic crop developed should be specifically evaluated
for the various environmental risks related to potential gene flow.
For an in-depth review of the reported discovery of transgenic
DNA found in Mexican maize, the controversy surrounding the studies,
and the possible consequences, please see our
discussion of GM Maize in Mexico. Additional information about
concerns of gene flow from transgenic crops:
Ellstrand, Norman C. 2001. When Transgenes Wander, Should We
Worry? Plant Physiology, Vol. 125, pp. 1543-1545, available at http://www.biotech-info.net/wandering_transgenics.html.
Does herbicide-tolerant Clearfield®
wheat, such as the cultivar 'Above' developed at CSU, incorporate
a transgenic trait?
Both transgenic and conventional crop varieties are sold under the
Clearfield® brand. Buyers should check the information provided
for the particular variety of interest.
'Above' wheat is not a transgenic cultivar. Researchers at American
Cyanamid, now part of BASF Corporation, identified the trait for
tolerance to imidazolinone (IMI) herbicides in a wheat plant after
exposure to a chemical mutagen. The herbicide tolerance trait was
transferred to adapted wheat cultivars by conventional crossing,
and 'Above' was subsequently selected from breeding populations
segregating for herbicide tolerance and other traits. The process
of induced mutagenesis used to develop the herbicide tolerance trait
is considered to be a conventional breeding technique, and 'Above'
is not considered to be genetically engineered or a genetically
BASF Corporation still owns the gene for IMI herbicide tolerance
that is used in 'Above'. More information about the 'Above' wheat
variety and the Clearfield® production system is available at http://wheat.colostate.edu/03116.html
(html file) or http://wheat.colostate.edu/03116.pdf
BASF Corporation also owns imidazolinone-tolerance genes used in
varieties of corn, canola, rice, and sunflower in addition to imidazolinone
tolerant wheat, like 'Above'. All are marketed as Clearfield® varieties.
The herbicide tolerance genes used in these crops also were individually
derived through mutagenesis (the sunflower IMI tolerance gene was
identified as a mutation in a natural population of sunflowers),
and varieties incorporating these genes alone are not transgenic.
Some confusion exists, however, because some corn varieties incorporate
both the IMI herbicide-tolerance gene and a transgenic trait, Bt-derived
insect resistance. These Clearfield® corn varieties are genetically
engineered, transgenic plants, but the herbicide tolerance is not
the transgenic trait. More information can be found on the BASF
website at http://www.clearfieldsystem.com/html/gmo.html.
Scott Reid at Colorado State University provided the content
for this page with funding from CSU Cooperative Extension.