2.1—Any DNA Insertion can cause a mutation
Any insertion of DNA into chromosomes can disrupt genes
Analysis of Peer-Reviewed Research:
It is certainly true that crop breeding changes DNA; in fact, that is the purpose of all breeding programs—to create differences in DNA. Campaigners who are opposed to GM crops consistently point to the potential harmful effects of DNA inserts, and the potential presence of multiple fragments of new DNA in a transformed plant. There are several problems with their assertions: 1) All plant chromosomes are repeatedly disrupted by many structural changes to DNA that have occurred in plants repeatedly over the course of recent history, and still occur today when plants are grown each season in the field; 2) All breeding technologies produce numerous changes and disruptions to the structure of plant chromosomes; 3) Conventional breeding techniques, accepted as safe by all, cause much more genetic disruption than those introduced by genetic engineering, and the resulting plants are not tested extensively for genetic change nor for safety attributes using the rigorous standards applied to genetically engineered plants.
Very rarely conventional crop breeders have indeed produced new crop varieties that have problems, such as celery that gives you skin rashes or potatoes that are potentially toxic. These unfortunate events are so rare and solved so quickly that hardly anyone has heard of them. The chances of a genetically engineered crop having such problems are far, far less likely, and because they are scrutinized so heavily, any problems that do occur would certainly be eliminated before reaching the market. Genetic Roulette is totally unrealistic about risks of DNA insertions.
A more balanced and science-based assessment comes from the European Commission, which has concluded that biotech/ GE foods are likely safer than conventional foods:
“Indeed, the use of more precise technology and the greater regulatory scrutiny probably make them even safer than conventional plants and foods; and if there are unforeseen environmental effects – none have appeared as yet – these should be rapidly detected by our monitoring requirements. On the other hand, the benefits of these plants and products for human health and the environment become increasingly clear.” ( European Commission 2001)
1. Trans-gene insertion can certainly cause mutations and can knock out genes or change the ways genes are expressed. What Genetic Roulette fails to tell the reader is that other forms of conventional breeding also create DNA insertions into chromosomes—often a much greater number than occurs when a single DNA fragment is inserted in the production of a transgenic plant using genetic engineering. Furthermore, random DNA alterations can also occur in wild plants because of exposure of plants to radiation in the fields and pastures, virus infection, movement of DNA parasites, and so on. For example soybeans have been found growing in the fields with alterations to flower color caused by disruptions that happened to occur in the soybean chromosomes that affected the genes involved in pigment formation (Zabala , Vodkin 2008). Many ornamental flowers display color transformations caused by genetic disruptions. Corn seeds often show changes in coloration or patterns of speckling that are the results of chromosomal rearrangements or disruptions to genes involved in seed color (Fedoroff 1989) and direct inspection of the DNA sequence in corn confirms the idea that corn chromosomes suffer numerous disruptions during evolution (Rutgers University Press Release 4th Oct 2006). There are several thousand chromosome disruptions identified in rice genomes caused by disruptive DNA parasites (Jiang and others 2004). These common variations are not harmful since not a single ill effect has ever been demonstrated to be the result of DNA alteration in a food or feed plant (Bejarano and others 1996; Harper and others 2002; Rutgers University 2006; Dooner and Weil 2007; Lisch 2005).
2. Developers of transgenic plants search for plants that have a single clean and complete gene insertion. There is no scientific evidence that multiple inserts of transgene DNA causes adverse effects, but in spite of this, transgenic food crops containing more than a single insert are no longer submitted to regulators for approval. Researchers can usually find transgenic plants with single functioning insert.
3. Odd variants are weeded out in the intensive selection process used in the development of genetically engineered crops. At each step in transgenic plant development the best individuals are selected from hundreds or thousands of others—often these will most closely resemble the variety into which DNA was inserted. Moreover, when a genetically transformed plant is selected for further development (and it may be selected from hundreds of potential candidates), it is put through a full battery of safety tests to ensure that no unintended adverse changes have taken place.(Kuiper and others 2001; McHughen 2000, Tribe 2008.) Regulatory agencies require data showing that the genetic modification is stably inherited, and that it is fully characterized to show it is not disrupting other gene functions in the transformed plant.
4. Conventional plant breeding shuffles DNA more than transgene insertion does. Modern genetic research shows that genes and larger fragments of DNA are frequently deleted, inserted, rearranged and mutated in chromosomes during conventional plant breeding. The magnitude of these unpredictable and unexpected changes far exceeds the more limited number of changes created by transgene insertion (Batista and others; 2008 Baudo and others; 2006 Shirley and others 1992). It is remarkable that in spite of all of the fearful statements made about the dangers of gene insertion and random gene shuffling, the numerous large and random disruptions of DNA that have historically occurred during crop development and among wild plant varieties have never been linked with an adverse outcome (Bejarano and others 1996; Harper and others 2002; Tanne , Sela 2005). Tribe D (2008)).
5. Evolution is a natural process that leads to continual changes in DNA. It is easy to think of evolution as something that happened in the past. The processes that drive evolution (DNA mutation, translocations, gene fusions, etc.) are still at work today. Each species of plant that we eat does not have one rigidly fixed genetic sequence—many DNA differences are found between different varieties of wheat, rice, corn and other common crops. We have already given examples of such differences in item 1 above, but many more could be given. Akio Kato and colleagues have shown, by using colored stains to paint chromosomes at the sites of DNA change, that in different corn varieties the same chromosomes are very different from one another. This staining of corn chromosomes visualizes great differences between cultivated varieties that can be seen directly in dividing root cells of this plant (Kato and others 2004). The same laboratory has shown that DNA traffic from cell organelles to the nucleus often permanently disrupts nuclear DNA by accidental insertion of new DNA into corn chromosomes (Lough and others 2008). Similarly, in papaya and other plants, DNA from chloroplasts disrupts chromosome structure by accidental insertion in novel locations (Ming and others 2008). These are just some examples of constant trafficking of DNA to new locations during evolution.
One source of much genetic change in plants is the combination of complete genomes from two different species to form what is called a polyploid, meaning possession of multiple sets of chromosomes. Polyploids are usually formed by cross pollination between two different plant species. Most people are unaware that such cross-pollination happens quite frequently in natural habitats, and that most food crops are polyploid (Leitch, Leitch 2008). When a polyploid crop plant, such as wheat, is newly formed, numerous additional disruptive genetic changes will often occur (Kashkush and others 2002). Pairing of whole sets of chromosomes that never before resided in the same organism to create a new polyploid crop, followed by the many additional genetic changes that occur after two different sets of different chromosomes are combined, is a far more radical disruption to a plant genome than the relatively conservative changes made by genetic engineers when they add a single trans-gene. The results have not only been safe, but hugely beneficial to humans.
Plant breeders use the results of evolution as their starting point. The many genetic disruptions of chromosomes that have occurred during evolution are present in conventionally bred crop varieties because breeders use a range of plant varieties to do their breeding. The extent of unexpected genetic disruption in food crops from this source of genetic change is greater than the disruption to the plant genome caused by genetic engineering.
Batista R and others (2008). Microarray analyses reveal that plant mutagenesis may induce more transcriptomic changes than transgene insertion. Proceedings of the National Academy of Sciences of the United States of America 105(9): 3640–3645.
Baudo MM, Lyons R, Powers S, Pastori GM, Edwards KJ, Holdsworth MJ, Shewry PR. (2006). Transgenesis has less impact on the transcriptome of wheat grain than conventional breeding. Plant Biotechnol J. 2006 Jul;4(4):369-80
Bejarano ER and others (1996). Integration of multiple repeats of geminiviral DNA into the nuclear genome of tobacco during evolution. Proc. Natl. Acad. Sci. U.S.A. 93:759– 764. www.pnas.org/content/93/2/759.
Dooner HK and Weil CF (2007). Give-and-take: interactions between DNA transposons and their host plant genomes. Current Opinion in Genetics & Development 2007, 17:486–492.
European Commission (2001). Press Release of 8 October 2001, announcing the release of 15 year study incl 81 projects/70M euros, 400 teams. (European Commission (2001). Press Release of 8 October 2001, announcing the release of 15 year study incl 81 projects/70M euros, 400 teams. European Commission (2001). Press Release of 8 October 2001, announcing the release of 15 year study incl 81 projects/70M euros, 400 teams. ec.europa.eu/research/fp5/eag-gmo.html and ec.europa.eu/research/fp5/pdf/eag-gmo.pdf
Fedoroff NV (1989). Maize transposable elements. In Mobile DNA. Editors Douglas E Berg and Martha M Howe. American Society for Microbiology
Harper G and others (2002). Review. Viral sequences integrated into plant genomes. Annual Review of Phytopathology 40:119–36.
Jiang N and others (2004) Pack-MULE transposable elements mediate gene evolution in plants. Nature 431, 569-573.
Kashkush K and others (2002). Gene loss, silencing and activation in a newly synthesised a wheat allotetraploid. Genetics 160:1651-1659.
Kato A and others (2004). Chromosome painting using repetitive DNA sequences as probes for somatic chromosome identification in maize. Proceedings of the National Academy of Sciences of the USA 101(37): 13554-13559 www.pnas.org/content/101/37/13554
Kuiper HA, Kleter GA, Noteborn HPJM , and Kok EJ (2001). Assessment of the food safety issues relating to genetically modified food.The Plant Journal 27;6):503-526. Perhaps the best scientifically professional introduction to the topic of genetically modified food safety. Free access at www3.interscience.wiley.com/journal/118986104/abstract?CRETRY=1&SRETRY=0
Leitch AR ,Leitch IJ (2008). Genome plasticity and the diversity of polyploid plants. Science 320:481-483.
Lisch D. (2005). Pack-MULEs: theft on a massive scale. Bioessays 27:353-355.
Lough A and others (2008) Mitochondrial DNA transfer to the nucleus generates extensive insertion site variation in maize. Genetics, 178: 47-55 doi:10.1534/genetics.107.079624
McHughen A (2000). A Consumer’s guide to GM food : From Green Genes to Red Herrings . (Published as Pandora’s Picnic Basket in the USA). Oxford. Arguably the best book for the general reader about whether it is safe to eat the GM food.
Ming R and others (2008). The draft genome of the transgenic tropical fruit tree papaya (Carica papaya Linnaeus). Nature 252:991-997
Rutgers University Press Release (4th Oct 2006). Genome archaeology illuminates the genetic engineering debate. www.eurekalert.org/pub_releases/2006-10/rtsu-gai100306.php accessed Dec 11 2008. A Summary of Bruggmann and others Genome Research 16:1241-1251.
Shirley BW and others (1992). Effects of ionizing radiation on a plant genome: analysis of two Arabidopsis transparent testa mutations. The Plant Cell 4, 333-347.
Tanne E, Sela I (2005). Occurrence of a DNA sequence of a non-retro RNA virus in a host plant genome and its expression: evidence for recombination between viral and host RNAs.Virology.332(2):614-22.
Tribe D (2008). Blog posting. Gene-chips prove transgenes are clean genes. gmopundit.blogspot.com/2008/07/gene-chips-prove-transgenes-are-clean.html
Tribe D (2008 a). Blog posting. Safety, safety, safety, and more GM food safety. The Food and Chemical Toxicology Sextet. gmopundit.blogspot.com/2008/06/safety-safety-safety-and-more-gm-food.html.
Zabala G, Vodkin L.(2008). A putative autonomous 20.5 kb-CACTA transposon insertion in an F3′H allele identifies a new CACTA transposon subfamily in Glycine max. BMC Plant Biology. Research article Open Access www.biomedcentral.com/1471-2229/8/124.
Foreign genes disrupt the DNA at the insertion site
1. When genes are inserted at random in the DNA, their location can influence their function, as well as the function of natural genes.
2. “Insertion mutations” can scramble, delete, or relocate the genetic code near the insertion site.
3. Evaluation of insertion sites have shown relocations of up to 40,000 DNA base pairs, mixing together of foreign and host DNA, large scale deletions of more than a dozen genes and multiple random insertions of DNA fragments.
Genetic Roulette discusses the potential hazards from insertion of DNA into chromosomes.