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Tuesday, June 4, 2013

The Process of Genetic Engineering


Institute for Respsonsible Technology

The most comprehensive source of GMO information on the web


The GE Process

 

Somatic embryos are embryos that originate in tissue culture in response to plant hormones added to the growth medium. Source: National Agricultural Biotechnology Centre, Uganda

 

What is a GMO?


A GMO (genetically modified organism) is the result of a laboratory process where genes from the DNA of one species are extracted and artificially forced into the genes of an unrelated plant or animal. The foreign genes may come from bacteria, viruses, insects, animals or even humans. Because this involves the transfer of genes, GMOs are also known as “transgenic” organisms.

This process may be called either Genetic Engineering (GE) or Genetic Modification (GM); they are one and the same.

What is a gene?


Every plant and animal is made of cells, each of which has a center called a nucleus. Inside every nucleus there are strings of DNA, half of which is normally inherited from the mother and half from the father. Short sequences of DNA are called genes. These genes operate in complex networks that are finely regulated to enable the processes of living organisms to happen in the right place and at the right time. 

How is genetic engineering done?


Because living organisms have natural barriers to protect themselves against the introduction of DNA from a different species, genetic engineers must force the DNA from one organism into another. Their methods include:
  • Using viruses or bacteria to "infect" animal or plant cells with the new DNA.
  • Coating DNA onto tiny metal pellets, and firing it with a special gun into the cells.
  • Injecting the new DNA into fertilized eggs with a very fine needle.
  • Using electric shocks to create holes in the membrane covering sperm, and then forcing the new DNA into the sperm through these holes.

Is genetic engineering precise?


The technology of genetic engineering is currently very crude. It is not possible to insert a new gene with any accuracy, and the transfer of new genes can disrupt the finely controlled network of DNA in an organism.

Current understanding of the way in which DNA works is extremely limited, and any change to the DNA of an organism at any point can have side effects that are impossible to predict or control. The new gene could, for example, alter chemical reactions within the cell or disturb cell functions. This could lead to instability, the creation of new toxins or allergens, and changes in nutritional value.

But haven't growers been grafting trees, breeding animals, and hybridizing seeds for years?


Genetic engineering is completely different from traditional breeding and carries unique risks.

In traditional breeding it is possible to mate a pig with another pig to get a new variety, but is not possible to mate a pig with a potato or a mouse. Even when species that may seem to be closely related do succeed in breeding, the offspring are usually infertile—a horse, for example, can mate with a donkey, but the offspring (a mule) is sterile.

With genetic engineering, scientists can breach species barriers set up by nature. For example, they have spliced fish genes into tomatoes. The results are plants (or animals) with traits that would be virtually impossible to obtain with natural processes, such as crossbreeding or grafting.

What combinations have been tried?


It is now possible for plants to be engineered with genes taken from bacteria, viruses, insects, animals or even humans. Scientists have worked on some interesting combinations:
  • Spider genes were inserted into goat DNA, in hopes that the goat milk would contain spider web protein for use in bulletproof vests.
  • Cow genes turned pigskins into cowhides.
  • Jellyfish genes lit up pigs' noses in the dark.
  • Artic fish genes gave tomatoes and strawberries tolerance to frost.
Field trials have included:
  • Corn engineered with human genes (Dow)
  • Sugarcane engineered with human genes (Hawaii Agriculture Research Center)
  • Corn engineered with jellyfish genes (Stanford University)
  • Tobacco engineered with lettuce genes (University of Hawaii)
  • Rice engineered with human genes (Applied Phytologics)
  • Corn engineered with hepatitis virus genes (Prodigene)
  • Potatoes that glowed in the dark when they needed watering.
  • Human genes were inserted into corn to produce spermicide.

Does the biotech industry hold any promise?


Genetic modification of plants is not the only biotechnology. The study of DNA does hold promise for many potential applications, including medicine. However, the current technology of GM foods is based on obsolete information and theory, and is prone to dangerous side effects. Economic interests have pushed it onto the market too soon.

Moreover, molecular marker technologies - so called Marker Assisted Selection (MAS) used with conventional breeding - show much promise for developing improved crop varieties, without the potentially dangerous side effects of direct genetic modification.


Frosted Flakes
Where are they?

In your food! First introduced into the food supply in the mid-1990s, GMOs are now present in the vast majority of processed foods in the US. While they are banned as food ingredients in Europe and elsewhere, the FDA does not even require the labeling of GMOs in food ingredient lists.
Although there have been attempts to increase nutritional benefits or productivity, the two main traits that have been added to date are herbicide tolerance and the ability of the plant to produce its own pesticide. These results have no health benefit, only economic benefit.


What foods are GM?

Currently commercialized GM crops in the U.S. include soy (94%), cotton (90%), canola (90%), sugar beets (95%), corn (88%), Hawaiian papaya (more than 50%), zucchini and yellow squash (over 24,000 acres).

Products derived from the above, including oils from all four, soy protein, soy lecithin, cornstarch, corn syrup and high fructose corn syrup among others. There are also many "invisible ingredients," derived from GM crops that are not obviously from corn or soy. Read more

Why should you care?

Rat IntestinesGenetically modified foods have been linked to toxic and allergic reactions, sick, sterile, and dead livestock, and damage to virtually every organ studied in lab animals. The effects on humans of consuming these new combinations of proteins produced in GMOs are unknown and have not been studied. See more under GMO Health Risks.

Crops such as Bt cotton produce pesticides inside the plant. This kills or deters insects, saving the farmer from having to spray pesticides. The plants themselves are toxic, and not just to insects. Farmers in India, who let their sheep graze on Bt cotton plants after the harvest, saw thousands of sheep die!
Herbicide tolerance lets the farmer spray weed-killer directly on the crop without killing it. Comparative studies on the toxic residues in foods from such crops have not yet been done.

Pollen from GM crops can contaminate nearby crops of the same type, except for soy, which does not cross-pollinate. In fact, virtually all heritage varieties of corn in Mexico (the origin of all corn) have been found to have some contamination. Canola and cotton also cross-pollinate. The long-term effects on the environment could be disastrous. See more under Environmental Dangers.


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Process of Developing Genetically Modified (GM) Crops

Genetic modification refers to techniques used to manipulate the genetic composition of an organism by adding specific useful genes. A gene is a sequence of DNA that contains information that determines a particular characteristic/trait. All organisms have DNA (genes). Genes are located in chromosomes. Genes are units of inheritance that are passed from one generation to the next and provide instructions for development and function of the organism. Crops that are developed through genetic modification are referred to as genetically modified (GM) crops, transgenic crops or genetically engineered (GE) crops.

The main steps involved in the development of GM crops are:
  1. Isolation of the gene(s) of interest: Existing knowledge about the structure, function or location on chromosomes is used to identify the gene(s) that is responsible for the desired trait in an organism, for example, drought tolerance or insect resistance.
  2. Insertion of the gene(s) into a transfer vector: The most commonly used gene transfer tool for plants is a circular molecule of DNA (plasmid) from the naturally occurring soil bacterium, Agrobacterium tumefaciens. The gene(s) of interest is inserted into the plasmid using recombinant DNA (rDNA) techniques. For additional information see Plasmids link
  3. Plant transformation: The modified A. tumefaciens cells containing the plasmid with the new gene are mixed with plant cells or cut pieces of plants such as leaves or stems (explants). Some of the cells take up a piece of the plasmid known as the T-DNA (transferred-DNA). The A. tumefaciens inserts the desired genes into one of the plant’s chromosomes to form GM (or transgenic) cells. The other most commonly used method to transfer DNA is particle bombardment (gene gun) where small particles coated with DNA molecules are bombarded into the cell. For additional information see Plant Transformation using Agrobacterium tumefaciens and Plant Transformation using Particle Bombardment links.
  4. Selection of the modified plant cells: After transformation, various methods are used to differentiate between the modified plant cells and the great majority of cells that have not incorporated the desired genes. Most often, selectable marker genes that confer antibiotic or herbicide resistance are used to favor growth of the transformed cells relative to the non-transformed cells. For this method, genes responsible for resistance are inserted into the vector and transferred along with the gene(s) conferring desired traits to the plant cells. When the cells are exposed to the antibiotic or herbicide, only the transformed cells (containing and expressing the selectable marker gene) will survive. The transformed cells are then regenerated to form whole plants using tissue culture methods.
  5. Regeneration into whole plants via tissue culture involves placing the explants (plant parts/cells) onto media containing nutrients that induce development of the cells into various plant parts to form whole plantlets (Figure 1). Once the plantlets are rooted they are transferred to pots and kept under controlled environmental conditions.
  6. Verification of transformation and characterization of the inserted DNA fragment. Verification of plant transformation involves demonstrating that the gene has been inserted and is inherited normally. Tests are done to determine the number of copies inserted, whether the copies are intact, and whether the insertion does not interfere with other genes to cause unintended effects. Testing of gene expression (i.e., production of messenger RNA and/or protein, evaluation of the trait of interest) is done to make sure that the gene is functional.
  7. Testing of plant performance is generally carried out first in the greenhouse or screenhouse to determine whether the modified plant has the desired new trait and does not have any new unwanted characteristics. Those that perform well are planted into the field for further testing. In the field, the plants are first grown in confined field trials to test whether the technology works (if the plants express the desired traits) in the open environment. If the technology works then the plants are tested in multi-location field trials to establish whether the crop performs well in different environmental conditions. If the GM crop passes all the tests, it may then be considered for commercial production.
  8. Safety assessment. Food and environmental safety assessment are carried out in conjunction with testing of plant performance. Descriptions of safety testing are described in the Food Safety Assessment and Environmental Safety Assessment links.
Further Reading
Figure 1: Regeneration of transgenic banana using tissue culture method


Somatic embryos are embryos that originate in tissue culture in response to plant hormones added to the growth medium. Source: National agricultural Biotechnology Centre, Uganda

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