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Sent: 22 June 2002 09:51
Subject: 68: Re: Risks of genetic engineering
This is from Neal Stewart, Racheff Chair of Plant Molecular Genetics, University of Tennessee, United States.
Dr. Verzola (message 67, June 21) and others miss the point of transgenics when they bring up the unintended consequence argument based on collateral mutations.
Let's use the example of software. If mutations arise in software and there is no selection, then there will be problems indeed. But what if there were ways to breed and select acceptable software? That is what happens in the plant biotech world.
Transgenic plants are much the same way. Mutations are introduced through transgenesis and tissue culture. Dozens, hundreds, or even thousands of transgenic events are made, and then the resulting plants are selected based upon expression of the gene of interest, and then on fertility and "normal" phenotypes. Just as in wide-cross or mutation breeding (conventional techniques), the one-to-few accceptable events are chosen. In that case it is the same. But since only one-to-a-few genes are introduced in transgenesis, then the risk is lower than the other techniques because of certainty. Coupled with the subsequent breeding that occurs post-transgenesis in which the transgene can be selected in new genetic backgrounds quite precisely, the genetic-based risk would drop even further relative to mutation breeding. Still, after a number of breeding events, the position effects become quite predictable. This is what has occured as the glyphosate resistance gene has been bred into many lines and commercial varieties of Roundup Ready soybean-- the 3-5% yield drag as the results of the original genetics varies very little.
We can do posthoc analyses on transgenic varieties in much more detail and therefore, know more about them than conventional varieties in days past. Microarray analysis and metanomic techniques can yield quite precise data on substantial equivalence. [metanomics is the study of gene expression at the metabolite level...Moderator]. But why stop at transgenic products? If these assays are required, then they should be required for every new variety and even old varieties that are grown. Then what is the baseline? Big can of worms...
Professor Neal Stewart,
University of Tennessee,
e-mail: jstewar5 (at) utk.edu
[This line of discussion is now cut, unless messages consider the consequences/relevance for gene flow...Moderator]
Sent: 22 June 2002 10:09
Subject: 69: Re: Gene flow risk assessment - plants
Professor Muir again. This is in response to Dr. Nickson (message 24, June 7). The discussion by Dr. Nickson on environmental risk assessment as a result of gene flow seems most reasonable and with some modification can be used in general for plants or animals. As he points out there are really two issues of gene flow:
1) probability the gene will spread into the environment (exposure) and 2) potential harms to the environment if the transgene spreads into the environment (i.e. harm given exposure).
The product of these probabilities results in risk. Addressing the second issue (harm given exposure) is very difficult (perhaps impossible) because all potential harms may not be known a priori. However, the first issue can be addressed by population genetics. Gene flow by pollen, seeds, or escaped animals, is only the first step. From there, natural selection will determine the fate of the transgene if the population size is large enough. The transgene may be eliminated resulting in no risk, or may increase in frequency, resulting in risk of the potential harms defined in step (2). A conservative method of risk assessment would be to address the issue of gene flow, which is something we can predetermine using science based methods, and only proceed with those products which suggest a low probability of spread. The second issue of potential harms then becomes mote. See http://www.isb.vt.edu/news/2002/news02.feb.html#feb0201 for more detail on this method. [This links to an article by Professer Muir, entitled "Potential environmental risks and hazards of biotechnology. Part II: Methods to estimate risks and hazards", in the February 2002 version of the Information Systems for Biotechnology (ISB) News Report...Moderator].
However I disagree with his conclusion "the current biotech products have shown no measureable risks compared to the risks already present from their traditionally grown counterparts. However, the lack of detectable effects and measurable hazards seems to have left some of the scientific community with a sense of uncertainty, possibly due to dissatisfaction with negative results."
I point you to the abstract of Stewart et al (1997): "Rapeseed Brassica napus L. transgenic for a Bacillus thuringiensis (Bt) transgene was developed and was shown to be insecticidal towards certain caterpillars including the diamondback moth Plutella xylostella L. and the corn earworm Helicoverpa tea Boddie. To simulate an escape of the transgenics from cultivation, a field experiment was performed in which transgenic and nontransgenic rapeseed plants were planted in natural vegetation and cultivated plots and subjected to various selection pressures in the form of herbivory from insects. Only two plants, both transgenic, survived the winter to reproduce in the natural-vegetation plots which were dominated by grasses such as crabgrass. However, in plots that were initially cultivated then allowed to naturalize, medium to high levels of defoliation decreased survivorship of nontransgenic plants relative to Bt-transgenic plants and increased differential reproduction in favour of Bt plants. Thus, where suitable habitat is readily available, there is a likelihood of enhanced ecological risk associated with the release of certain transgene/crop combinations such as insecticidal rapeseed. This is the first report of a field study demonstrating the effect of a fitness-increasing transgene in plants." (Stewart CN, All JN, Raymer PL, Ramachandran S. 1997. Increased fitness of transgenic insecticidal rapeseed under insect selection pressure. Molecular Ecology 6:773-779).
This report is critical because it shows that it is possible to modify an organism in the laboratory to have an increased fitness in natural settings and refutes the notion that any man-made modification to an organism will always reduce fitness as has been suggested elsewhere.
William M. Muir, Ph.D.
1151 Lilly Hall
W. Lafayette, IN 47906
bmuir (at) purdue.edu