GMO DNA>About the GMO technology
About the GMO technology
What is genetically modified DNA?
Genes and their promoters (on/off switches in front of the genes) are rearranged and copied and pasted together (using enzymes) into a convenient condensed form in the laboratory. It is usually constructed in a self replicating circular piece of DNA called a plasmid that can replicate in bacteria.
When the construction process is done, the plasmid is purified from the bacteria and inserted into the host organism by a variety of methods. A common technique with plants is to then insert the plasmid back into Agrobacterium tumefaciens (where it came from originally) and grow the bacteria along with cells of the recipient plant (co-cultivate). The bacteria naturally transfer their DNA into the plant and the plants are screened for presence of the inserted DNA and the expression of the gene of interest (GOI). In plants the plasmid DNA usually inserts itself into the chromosome DNA at random places.
The image at the top right shows a normal non-engineered plasmid from the bacterium Agrobacterium tumefaciens. The lower image shows how the plasmid is rearranged into two plasmids with different regions added for ease of cloning and construction and for the gene that is to be expressed in plants (GOI).
How is it detected?
To detect the presence of the inserted DNA there are a number of strategies. All of them involve isolating DNA from the plant and performing PCR to copy the region of interest.
To amplify a region of interest, short pieces of DNA called primers are designed by the user and then synthesized by a company. Two primers are needed - a forward primer and a reverse primer. The primers are designed to match exactly the edges (left edge and right edge) of the region of interest. In the PCR reaction, the DNA is copied between the specific regions where the primers bind.
The tests that are offered for corn are designed so that one edge of the region of interest is in the foreign inserted DNA region, and the other edge is in the plant's normal DNA. This method detects one of the integration sites of the inserted DNA.
Why the concern about GMOs?
There are a number of concerns about this technology.
1. Often the plasmids contain genes that code for a toxin that is intended to act on insects that eat the plant. However, the toxins may affect other insects, as well as animals and people.
2. Plasmids that have a gene to confer resistance to an herbicide encourage the widespread use of the herbicide, which creates lasting toxic effects in the soil, changing the microbiology of the soil, and also systemically weakens the plant, not to mention systemic effects in animals and people.
3. Pollen from the GMO plants can spread into other fields, contaminating organic fields.