Transgenic (=Genetically Modified) Crops

I. Transgenic Plants

A.  General

• contain genes from another plant

• genetically modified � or GM crop

• in a sense, all crops are genetically modified from wild state by process of domestication via selective breeding and selection

B.  How to make a transgenic plant?

DNA isolated → restriction enzyme cuts up DNA → pieces of DNA isolated with gene of interest → DNA sequence modified to include markers (punctuation marks, add a promoter and termination sequence) → insert into plant → select transgenic individuals → regenerate new plant

C.  Inserting Genes

• Gene �gun�  (especially used in corn and rice)

• Ti plasmid � from Agrobacterium tumefaciens, causes crown gall, can insert its DNA into host plant which becomes incorporated into host chromosome

D.  Selecting genetically modified individuals.
    Only a small percentage of treated cells/plants actually become genetically modified by the process.  Thus, these must be identified.  Usually associate a marker gene with the gene construct.  This marker is usually for antibiotic or herbicide resistance.  If the cell/plant was transformed by the transgene, then it will survive when grow on a medium containing antibiotic or herbicide.
 

II.  Regulation of GMO�s

• institutional safety committees

• USDA � APHIS (federal plant pest act; regulate organisms likely to become pests/weeds

• FDA � oversees safety of foods

• EPA � regulate for pest resistance

• World Trade Organization � regulates commerce/sale

III.  Examples of GMO�s

1. Roundup resistant crops

2. Bt crops � Bacillus thuringensis contains a gene called Cry that produces a crystalline protein.  Once eaten, in an animal gut is is converted to a toxin (endotoxin) that kills assorted insects including maize corn borer, tobacco budworm and others on cotton, Colorado potato beetle.  The Good News � dramatic reduction in amount of chemicals used on fields.  The Bad News � can potentially kill monarchs (see case study) and possibility of resistance gene spreading.
   
       One way to avoid resistance, farmers required to plant 20% of fields in non-Bt corn so that there will be large enough population of Bt susceptible species to mate with and swamp out any Bt resistant individuals.

3. Lots of others

 IV.  Potential Problems

 A.  Human health issues

• allergenic reactions

• antibiotic resistance

• transfer of antibiotic resistance to other organisms

• enzymes could inactivate antibiotics

 B.  Environment

• crop-gene flow

 C.  Impact on crop technology

V.  Some ethical issues

A.  Terminator.
    Gene that cause the embryo to die.  The main purpose is to protect the patent so farmer can�t collect seeds and replant without buying more genetically modified crops. 

• Pro � crops won�t spread, companies protect patent

• Con � if spreads, kills embryo of neighboring plants (crop and wild), small farmers can�t afford

VI.  Risk/Benefit Analysis

A.  Risk assessment - Identify and define risks

• What could go wrong?

• How likely it is to occur?

• How harmful if it does?

B.  Risk = hazard x exposure; amount of risk = (hazard x exposure)/safeguards

C.  Benefits

• Does it save lives or is an improvement?

• Does it improve quality of life?

• Does it solve a problem?

• Does it increase efficiency?

• Who derives a benefit?

D.  Information Analysis

• Is it information vs. propaganda?

• Peer-reviewed vs. other?