4.3—Genes rearrange naturally all the time with no ill effects
Over evolutionary (very long) time scales, genes are unstable and rearrange. Sometimes dramatically.
Analysis of Peer-Reviewed Research:
These are amazing claims for which no evidence is provided. It is true that gene insertion by transformation can result in the presence of multiple DNA fragments in the plant–some of which may cause mutations. All plants contain many copies of repeated sequences that can and do serve as sites of rearrangement. Genetic Roulette overlooks the fact that during breeding and planting of crops these same kinds of changes occur and none has ever been linked to any adverse effect. Said another way, such changes in DNA have never been associated with real harms. Transgenic crops are subjected to a thorough safety assessment that includes a demonstration of required genetic stability prior to approval. Conventionally bred and organic crops that carry far more mutations are not subjected to safety review.
1. Repeated sequences can serve as sites for rearrangement and may appear to be unstable. All living cells have systems that allow DNA to be shuffled and rearranged. This process, called recombination, most often occurs between two identical sequences that are separated on a chromosome or are located on different chromosomes (Lewin 2008, Walker and other 1995). DNA rearrangements are major drivers of evolution and are common to all cells (Kidwell and Lisch 2002, Pennisi 2007). During the transformation of DNA into cells it is possible for more than one piece of DNA to be inserted. Sometimes these pieces are repeated copies of the intended insert and sometimes they are simply partial fragments. Scientists try to avoid plants that carry multiple DNA insert copies or extra DNA fragments. While most of the plants selected for further research carry a single copy of the intended insert occasionally plants with “extra” fragments are selected (Belgian Biosafety Server (2006). These “extra” fragments appear not to adversely affect stability; remember that all plants have hundreds of repeated sequences that are targets for instability throughout their chromosomes.
2. Stability is necessary for a transgenic crop to be useful. Crops vary greatly with regard to their genetic stability. The general principle that has been applied to GM crops is that they must be demonstrated to be at least as stable as other varieties of that same crop. GM crops are tested in greenhouses and experimental fields in order to evaluate a number of factors such as performance, the proper function of the newly introduced trait, and that the trait is stably inherited. It is difficult, if not impossible, to consistently grow the large quantity of seeds that will be needed for planting every year if the new variety is not stable. And, from a regulators’ point of view, if a new variety is not as stable as other plants of the same kind, there is no guarantee that it will remain safe for consumers and the environment. Genetic Roulette fails to acknowledge that most productive farmers in the world today buy new high quality seeds to plant each year—even poor farmers in developing countries buy seeds. Seed companies work hard to ensure minimal variation in performance from year to year.
3. There is no evidence that instability is greater in transgenic crops. Genetic Roulette relies on the statements of well known anti GM activists who claim that GM plants are particularly unstable, but this is not the consensus of peer reviewed scientific publications. This section of Genetic Roulette presents no evidence of transgene genetic instability, while credible scientific articles that describe genuinely unstable plant genes — for instance the genetically unstable R locus in maize which influences corn colour — report measurable rates of instability (Walker and others 1997). Practical experience with planting of over 500 million hectares of GM crops tells us that they are stable enough to function very well in farmers fields. Carrying the lack of evidence to the extreme, Smith audaciously speculates that the many ills he attributes to GM crops in Section 1 (dead cows and sheep, sick farmers, farmer worker allergies, etc) to the possible rearrangement of the GM crops genes – what Smith calls GM “crops gone bad”. Recall that in our response to Section 1 we showed that there was no association between GM crops and the misfortunes that Smith tells us about in Section 1—often the claimed events were not out of the ordinary. (Similar claims of genetic instability are made by Smith in Sections 4.2 and 2.6 of Genetic Roulette, and we discuss the issue in analyzing those claims.).
Belgian Biosafety Server (2006). Molecular characterisation of the genetic maps of commercial genetically modified plants. www.biosafety.be/gmcropff/EN/TP/MGC.html accessed Dec 26 2008. Provides description of DNA inserts in transgenic crops.
Kidwell MG and Lisch DR (2002). Transposable elements as sources of genomic variation. Chapter 5 in NL Craig and others. Mobile DNA II. ASM Press.
Lewin B (2008). Genes VIII. Jones and Bartlett. www.ergito.com/
Pennisi E (2007). Jumping genes hop into the evolutionary limelight. Science 317(5840):894 – 895. With genomes from ancient fish to modern humans in hand, researchers are gaining new respect for the role transposable elements play in evolution.
Walker EL, Robbins TP, Bureau TE, Kermicle J and Dellaporta SL (1995). Transposon-mediated chromosomal rearrangements and gene duplications in the formation of the maize R-r complex. EMBO J. 14(10):2350-63. Rearrangement of DNA induced by transposon can generate useful traits for plants. The resulting biodiversity is a good thing.
Walker EL, Eggleston WB, Demopulos D, Kermicle J and Dellaporta SL. Insertions of a novel class of transposable elements with a strong target site preference at the R locus of maize. Genetics 146:681-683. Transposons are involved in some genetic instability.
Transgenes are unstable and rearrange over time
1. At least two studies showed that the sequence of inserted genes was different than what was described by the company.
2. This suggests that transgenes are unstable and spontaneously rearrange.
3. The GM protein may therefore change, with unpredictable consequences for health
4. If so, safety assessments conducted on the original protein do not apply to the new version.
Smith asserts that inserted transgenes are inherently unstable and that through DNA rearrangements, new and potentially toxic proteins might be formed.