Transgenic Recombinant Food

        Transgenosis technology is a kind of modern technology in molecular biology, which is used to transfer genes from one species into another so as to reconstruct the genetic materials of the receiving species for the improvement of its properties, quality of nutrition in line with the need of human beings. The transgenic species as immediate food and food processed from transgenic species are called transgenic food.

        In other words, transgenic food are those directly made from or processed from the species (animals, plants and microorganisms, etc.) which can produce substances possessing highly effective expressions, such as polypeptide and protein, after one or several types of exogenous genes are transferred into it through the means of genetic engineering.

        The basic principle of transgenosis is easy to understand. It bears some similarity with common hybridization. The difference only lies in that hybridization transfers the whole chain of genes (chromosome), while transgenosis only selects the most useful section of genes to transfer. In this sense, transgenosis has a higher standard in selectivity.

Categories of transgenic food:
        In order to enhance the nutritious value of agricultural products and produce food faster and more effectively, scientists are adopting transgenosis technology to alter genetic data and reassemble new genes of species. The technology helps to obtain new transgenic food continuously and meanwhile enables food to be of higher nutrition, stronger preservability, and sounder resistibility to illnesses, insect pest and herbicide.

The first category----transgenic plant food product.
There are various kinds of transgenic plant foods, such as high protein wheat used to bake breads. To reverse the situation that wheat in the current market contains low rate of protein, protein genes possessing highly effective expressions are transferred into wheat, so that bread made from the wheat can be of more nutritious value.

        Another example is tomato, which is of rich nutrition, high economic value but weak preservability. It is discovered by researchers that ACC synthase gene as controlling factor is the major cause for decaying of plants. If the expression of the gene can be inhibited by the means of generic engineering, biosynthesis of ACC will be curbed so that plants won't soften and rot so easily. At present, with the joint efforts of many scientists from different countries, such as America and China, a novel variety of tomato which characterizes in strong resistibility to decaying and to softening, and sound preservability comes out. These characters enable long-distance transportation of the fruit and reduction of waste in its processing and transportation.

The second category---transgenic animal food product
        There are a variety of transgenic animal food products too, such as transgenic milk and pork. For example, cows into which certain gene from human body is transferred can produce milk with special gene. After abstraction it can be used to cure human diseases. While pigs into which a kind of growth factor gene of human is transferred can grow at twice speed of ordinary pigs. And the quality of the pork is improved. Such a kind of transgenic pork is now a delicious dish on the tables of Australian families.

The third category---transgenic microorganism food product
        Microorganisms are the most common material for transgenosis. Therefore, the cultivation and application of transgenic microorganisms are much easier. For instance, usually rennin for the production of cheese could only be abstracted from the stomach of the killed calf. Nowadays, with transgenosis technology and transgenic microorganisms, rennin can be obtained outside of the body, avoiding the mass killing of calves and diminishing the cost.

The forth category---special transgenic food product
        Special transgenic food products refer to our common corps, greens and fruits that have been processed by the means of genetic engineering to contain magic edible vaccines for the purpose of guarding against certain diseases. A typical example is a type of clove containing a cholera vaccine. Fed with the clover, mice can greatly increase disease resistance. In addition, the cholera vaccine can not only stand stomach acid, but also activate body’s immunity to cholera. Now, more and more researches are being conducted to transfer anti-disease genes into plants, to enable people to defend against diseases while enjoying freshness and sweetness of fruits and vegetables.

Outline the method used to create transgenic recombinant food. Include diagrams to illustrate the method.

        Figure 1. Overview of how transgenic crops are created.

        For many years plant breeding entailed the selection of the finest plants to get the best crops. In those days, variation occurred through induced mutation or hybridization where two or more plants were crossed. Selection occurred through nature, using a “selection of the fittest” concept, where only the seeds best adapted to that environment succeeded.


         For example, farmers selected only the biggest seeds with non-shattering seed heads, assuming these to be the best. Today, scientists can not only select, but also create crops by inserting genes to make a seeds bare any trait desired.
In order to make a transgenic crop, there are five main steps: (1)extracting DNA, (2)cloning a gene of interest, (3)designing the gene for plant infiltration, (4)transformation, and finally (5)plant breeding (see Figure 1).


        To understand this process, one must first known a bit about DNA (deoxyribonucleic acids). DNA is the universal programming language of all cells and stores their genetic information. It contains thousands of genes, which are discrete segments of DNA that encode the information necessary to produce and assemble specific proteins. All genes require specific regions in order to be utilized (or expressed) by a cell. These regions include (see Figure 2):
1. A promoter region, which signals where a gene begins and it used to express the gene;
2. A termination sequence, which signals the end of a gene;
3. And the coding region, which contains the actual gene to be expressed.
All these regions together allow a gene to create a protein. Once a gene is transcribed into a protein, it can then function as an enzyme to catalyze biochemical reactions or as a structural unit of a cell, both of which will contribute to the appearance of a particular trait in that organism.


        Figure 2. Gene Regions.

         All species are capable of turning DNA into protein through a process known as translation. This capability makes it possible to artificially put genes from one organism into another-a process generally termed transgenics. But just isolating random DNA and inserting it into another organism is not practical. We must first know what particular segments of DNA, and in particular what genes, to insert. Unfortunately, with reference to producing new crops, not much is known about which genes are responsible for increased plant yield, tolerance to different stresses and insects, color, or various other plant characteristics. Much of the research in transgenics is now focused on how to identify and sequence genes contributing to these characteristics.

         Genes that are determined to contribute to certain traits then need to be obtained in a significant amount before they can be inserted into another organism. In order to obtain the DNA comprising a gene, DNA is first extracted from cells and put into a bacterial plasmid. A plasmid is a molecular biological tool that allows any segment of DNA in be put into a carrier cell (usually a bacterial cell) and replicated to produce more of it. A bacterial cell (i.e. E. coli) that contains a plasmid can put aside and used over and over again to produce copies of the gene the researcher is interested in, a process that is generally referred to as “cloning” the gene. The word “cloning” referring to how many identical copies of the original gene can now be produced at will. Plasmids containing this gene can be used to modify the gene in any way the researcher sees fit, allowing novel effects on the gene trait to be produced (see Figure 1).

         Once the gene of interest has been amplified, it is time to introduce it into the plant species we are interested in. The nucleus of the plant cell is the target for the new transgenic DNA. There are many methods of doing this but the two most common methods include the “Gene Gun” and Agrobacterium method.

         The “Gene Gun” method, also known as the micro-projectile bombardment method, is most commonly used in species such as corn and rice. As its name implies, this procedure involves high velocity micro-projectiles to deliver DNA into living cells using a gun [1]. It involves sticking DNA to small micro-projectiles and then firing these into a cell. This technique is clean and safe. It enables scientists to transform organized tissue of plant species and has a universal delivery system common to many tissue types from many different species1. It can give rise to un-wanted side effects, such as the gene of interest being rearranged upon entry [1] or the target cell sustaining damage upon bombardment. Nevertheless, it has been quite useful for getting transgenes into organisms when no other options are available.

        Figure 3. Transfer DNA on a plasmid in Agrobacterium

         The Agrobacterium method involves the use of a soil-dwelling bacteria known as Agrobacterium tumefaciens, which has the ability to infect plant cells with a piece of its DNA. The piece of DNA that infects a plant is integrated into a plants chromosome through a tumor-inducing plasmid (Ti plasmid), which can take control of the plant’s cellular machinery and use it to make many copies of its own bacterial DNA. The Ti plasmid is a large circular DNA particle that replicates independently of the bacterial chromosome [1] (see Figure 3).


         The importance of this plasmid is that it contains regions of transfer DNA (tDNA), where a researcher can insert a gene, which can be transferred to a plant cell through a process known as a floral dip. A floral dip involves dipping flowering plants into a solution of Agrobacterium carrying the gene of interest, followed by the transgenic seeds being collected directly from the plant. This process is useful in that it is a natural method of transfer and therefore thought of as a more acceptable technique. In addition, Agrobacterium is capable of transferring large fragments of DNA very efficiently without substantial rearrangements, followed by maintaining high stability of the gene that was transferred . One of the biggest limitations of Agrobacterium is that not all important food crops can be infected by this bacteria.

Other methods
Some of the techniques used to transfer foreign cells into animals and plants include:
• Bacterial carriers
• Biolistics
• Calcium phosphate precipitation
• Electroporation
• Gene silencing
• Gene splicing
• Lipofection
• Microinjection
• Viral carriers.
Bacterial carriers
The bacterium Agrobacterium can infect plants, which makes it a suitable carrier for delivering DNA. The bacterium is prepared in a special solution to make its cell walls more porous. The selected gene is inserted into a bacterium extra chromosomal DNA molecule (called a plasmid) and dropped into the solution. The solution is heated, which allows the plasmid to enter the bacterium and express the new gene. The genetically altered bacterium (or recombinant) is allowed to recover (is ‘rested’) and grow and, depending on the plasmid, make extra copies of the new gene. The bacterium is then allowed to infect the target plant so it can deliver the plasmid and the new gene.

Biolistics
The selected DNA is attached to microscopic particles of gold or the metal tungsten. Like firing a gun, these DNA-laden particles are shot into the target cells using a burst of gas under pressure.

Calcium phosphate precipitation
The selected DNA is exposed to calcium phosphate. This mixture creates tiny granules. Target cells respond to these granules by surrounding and ingesting them (endoocytosis), allowing the granules to release the DNA and deliver it to the host nuclei and chromosome(s).

Electroporation
The prepared target cells are immersed in a special solution with the selected DNA. A short but intense electric shock is then passed through the solution. The result is small tears in the cell walls, which allow the new genetic material access to the nuclei. Then, the cells are placed into another solution and encouraged to repair their breached walls, locking the ‘donor’ DNA inside the cell. The selected DNA is incorporated into the host chromosomes to provide the host with a new gene.

Gene silencing
The gene responsible for the organism’s undesirable trait is identified. One method of ‘silencing’ that particular gene is to attach a second copy of the gene the wrong way around. This technique is used to prevent plants like peanuts and wheat from producing the proteins (allergens) commonly responsible for human allergies.

Gene splicing
Bacteria contain restriction enzymes that form part of the bacterium’s ‘immune system’ against invasion by another organism or bacteriophage (a bacterial virus). The restriction enzymes attack the foreign DNA by cutting it into precise sections and preventing it from being inserted into the bacterium’s chromosome.

Different bacteria produce different restriction enzymes that cut any DNA at different places, making the DNA ‘sticky’ in some cases, which means they can be ‘pasted’ directly onto the target organism’s prepared DNA.

Using these restriction enzymes from bacteria, molecular biologists can ‘genetically engineer’ the DNA for ‘insertion’ into target (host) cells to modify gene traits. The molecular biologist then uses another enzyme (ligase) to fuse the new gene into the chromosome.

Alternatively, instead of ‘pasting’, the new gene may be inserted into a bacterium’s extra chromosomal DNA molecule (a plasmid), which carries invasion genes that allow it to invade the target cell and deliver the gene.

Lipofection
Small bubbles of fat called liposomes are used as the carriers of selected DNA. The target cells and the liposomes are placed into a special solution. The liposomes merge with the cell membrane, allowing the DNA into the cells for inclusion in the chromosome.

Microinjection
The selected DNA is injected into a fertilised ovum (female egg cell) through an extremely slender device called a glass capillary tube. The genetically modified egg is then transplanted into the prepared uterus of a receptive female and allowed to grow to term. This method ensures that almost every cell in the developing organism’s body contains the new DNA but not every progeny carries the transgene (is deemed a ‘transgenic’ animal).

Viral carriers

A virus that will invade the target cells but not cause damage or death is chosen. The selected DNA is added to the genetic makeup of the virus, and then the virus is allowed to infect the target. As the virus invades cells and replicates, the selected DNA is added to the target cells.

Examples of genetically modified foods

Some current examples include:
• Crops are genetically engineered to be resistant to particular insect pests. For example, toxin genes (Bt toxin) from a bacterium found in soil (Bacillus thuringiensis) are inserted into the crop DNA so that the plants produce toxins specifically deadly to the larvae of their pest insects.

• Soybeans have been genetically modified to resist herbicides that would normally kill them.

• Plants are genetically modified to ensure longer shelf life or greater resistance to frost.

• Farm animals (such as pigs, cows and chickens) are genetically modified for faster growth rates, leaner muscle-to-fat ratios or superior resistance to disease.

• Plants are modified to yield higher protein or nutrient levels, or produce healthier oils containing ‘functional food’ components such as omega 3 fatty acids.

• Genetically modified cows can produce milk that contains higher levels of bioactive milk proteins or human blood clotting components or a human breast milk component.

Advantages and Disadvantages of Transgenic Recombinant Food

Benefits

• Crops
o Enhanced taste and quality
o Reduced maturation time
o Increased nutrients, yields, and stress tolerance
o Improved resistance to disease, pests, and herbicides
o New products and growing techniques

• Animals
o Increased resistance, productivity, hardiness, and feed efficiency
o Better yields of meat, eggs, and milk
o Improved animal health and diagnostic methods

• Environment
o "Friendly" bioherbicides and bioinsecticides
o Conservation of soil, water, and energy
o Bioprocessing for forestry products
o Better natural waste management
o More efficient processing

• Society
o Increased food security for growing populations


Controversies

• Safety
o Potential human health impacts, including allergens, transfer of antibiotic resistance markers, unknown effects
o Potential environmental impacts, including: unintended transfer of transgenes through cross-pollination, unknown effects on other organisms (e.g., soil microbes), and loss of flora and fauna biodiversity

• Access and Intellectual Property
o Domination of world food production by a few companies
o Increasing dependence on industrialized nations by developing countries
o Biopiracy, or foreign exploitation of natural resources

• Ethics
o Violation of natural organisms' intrinsic values
o Tampering with nature by mixing genes among species
o Objections to consuming animal genes in plants and vice versa
o Stress for animal

• Labeling
o Not mandatory in some countries (e.g., United States)
o Mixing GM crops with non-GM products confounds labeling attempts

• Society
o New advances may be skewed to interests of rich countries

Benefits in curbing food shortage proboems

        After the transgenic recombinant food are introduced, more or less it helps to curb the food shortage problem but not the ultimate solution for it. Transgenosis can help to reduced the maturation time and improved the crop resistance to disease, pests and herbicides. Hence, it will help to solve certain level of food shortage problem. However global political factors, uncertain climates and weather are also part of the factors to be consider while curbing the food shortage problem.

Impacts on economics sector of a country

        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:
• 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.

        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.

Hidden risks and benefits for human health

        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 conventional counterparts
• 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.

        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.

        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.

        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. A more detailed discussion of concerns about food allergies resulting from transgenic crops is available in our discussion of allergies.

Possible environmental hazards

        A concern about whether transgenic crops cause damage to the natural environment. One example includes pollen from transgenic corn, which has been suggested to kill the Monarch butterfly larvae. It has been shown that hybrid corn expresses a bacterial toxin in its pollen, which is then dispersed over 60 meters by wind. In this range, the corn pollen is deposited on other plants near cornfields where it can be ingested by non-target organisms including the monarch butterfly. These butterflies have been found to eat less, have a slower growth rate and higher death rate . A second example is the hybridization of crops with nearby weeds. This could cause these weeds to attain resistance to herbicides or other things that we have been trying to avoid for many years. Genes that provide resistance to viral disease or other traits allowing them to survive in their environment could end up benefiting weed populations around a crop field. This trait could make that population more difficult to control. To date, there has been little evidence to support this theory.

        On other side of the coin are the notions that support the use of transgenic crops. The potential benefits of which are quite obvious, including such things as increased yields (to feed a growing population), decreasing the use of pesticides (to save the environment and the cost of pesticides), and the production of novel crops (such as providing crops with increased nutritional value) . Being able to retrofit any crop to our desires is a powerful concept, especially with the changing climates of today.

        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 over time.

Reported cases of non-genetically modified organisms developing increased resistance to pesticides

        A concern about what affect genetically modified material could have on human health. For example, transgenic crops have been suggested to cause allergies in some people, although it is uncertain whether transgenic crops are the source of this reaction .Furthermore the antibiotic resistance genes placed in these crops has been suggested to cause resistance to antibiotics leading to super bugs that cannot be killed with antibiotic treatments . The idea of a population being uncomfortable with ingesting DNA that originated from another source, such as a virus or bacteria, must also be considered when thinking about producing transgenic crops. However, to date, there is no evidence of the DNA from transgenic crops being any different from the DNA ingested from conventional crops.

        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. 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 general conclusions:

• 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.

• 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 low.

• 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.