Genetically Modified Crops: Methods and Safety

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Genetically Modified Crops Methods and Safety

• Prepared by Tracy Boehmer
• April 14, 2003

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Overview

• For thousands of years, farmers have been
  altering the genetic makeup of crops by using
  human selection to improve growth time, size,
  etc.
• World needs to consume over 2 billion tons a year
  of wheat, rice, maize, barley, and other crops
• Genetically Modified Crops have the potential to
  feed the world

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What is a Genetically Modified Crop?

• The modification of the genetic characteristics
  of a microorganism, plant or animal by inserting
  a modified gene or a gene from another variety or
  species.
• Synonyms
• Genetically Modified Organism (GMO)
• Genetically Engineered Organism (GEO)
• Transgenic Organism
• Transgenic indicates gene transfer using
  recombinant DNA technology. The transferred gene
  is usually, but not necessarily, from outside the
  normal range of sexual compatibility.

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What Crops have been Genetically Modified
Lettuce
Corn
Carrot
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Producing Transgenic Plants

• Isolate and clone gene of interest
• Add DNA segments to initiate or enhance gene
  expression
• Add selectable markers
• Introduce gene construct into plant cells
  (transformation)
• Select transformed cells or tissues
• Regenerate whole plants

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Isolation of Gene of Interest

• Look for an organism in which the operation has
  the greatest chance of being successful and easy
• Develop a Gene Library
• Use functional complementation to find desired
  gene
• A mutant colony (organism incapable of
  realizing one function) and the plasmids
  extracted from the colony. The mutant colony
  will recover the plasmid that will help restore
  the function. The recovered plasmid is then the
  source for the gene.

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Add DNA segments to initiate or enhance gene
expression

• Promoter initiates transcription affects when,
  where, and how much gene product is produced.
• Termination sequence marks end of gene.
• Marker gene is added
• Usually resistant to an herbicide or
  antibiotics
• Used to verify the incorporation and expression
  of the transgene

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Techniques of Gene Transfer

• Gene Gun Method-Cells are bombarded with
  particles that are coated with the DNA containing
  plasmid by a flow of Helium. The plasmid is
  transferred into the plant cell and is put into
  its genome by enzymatic activity
• Agrobacterium Method-Contains a piece of DNA
  called the Ti-plasmid that can move from the
  Agrobacterium into a plant. The gene is isolated
  and inserted into the Ti-plasmid. The modified
  plasmid is placed into the Agrobacterium and then
  is transferred to the plant.

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Safety Issues

• Health
• Toxicity
• Allergenicity
• Antibiotic Resistance Markers
• Environment
• Pest Resistance
• Effect of Nontarget Organisms
• Creation of Super Viruses
• Gene Flow and Superweeds

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Health Safety

• Toxicity- Substantial Equivalence used to
  demonstrate that a GM food possesses similar
  levels and variations in critical nutrients and
  toxicants as the unaltered foods
• Allergenicity- If GM food contains the product of
  a gene from a source with known allergenic
  effects, the gene product should be assumed to be
  allergenic
• Antibiotic Resistance Markers- Markers used in GM
  foods could incorporate themselves into other
  environmental or gut microorganisms

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Environmental Safety

• Pest Resistance- Could develop superpests
• Effects of Nontarget Organisms- Monarch Butterfly
  
• Creation of Superviruses- When organisms are
  changed to guard against certain viruses, new
  viruses will form
• Gene Flow and Superweeds- Possibility of
  hybridization of transgenic pest-protected plant
  with neighboring wild relatives

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Conclusion

• Long Term Effect are Unknown
• The Many Benefits of Genetically Modified Crops
  usually Outweigh the Potential Risk