Science in Society Archive

GM Crops May All Be Unstable

I-SIS has drawn attention to the instability of GMOs and GM constructs all along. Prof. Joe Cummins offers this latest verdict, all GM crops may be unstable.

It is repeatedly claimed that genetically modified (GM) crops are altered with single genes that are stable and equivalent to the genes that have been selected and bred into the crops. In every case the GM crops originated from cell cultures that have been know to be vexed with a phenomenon called somaclonal variation. Somaclonal variation has been encountered in genetic transformation using both biolistic and Agrobacterium transformation followed by cell culture to isolate desirable agricultural characteristics. The phenomenon is that cell cultures leading to isolate individual clones and plants are plagued by genetic instability caused both by gene mutation and chromosome rearrangement. In extreme responses plants may be infertile and the extensive mutation leads to undesirable toxic natural products being produced. Furthermore, the transgenes introduced into the modified crop are recognized as invaders by the crop being transformed and the invading genes are silenced by mechanisms including DNA methylation or gene inactivation at transcription.

The evidence that the genetic instability resulting in somaclonal variation is caused by activation of inactive virus like genetic elements called transposons is currently very compelling (see Courtial et al 2001). Activated transposons create both gene mutation and
chromosome rearrangement. On top of the somaclonal impact the inserted transgenes are frequently silenced (see Demeke et al 1999). Even the most widely distributed commercial GM crops such as Roundup Ready soy were found to contain unexplained DNA sequences in the gene for herbicide resistance after ten years of cultivation (Palevitz 2000). The
promised peer review publication on the aberrant DNA sequences was not located and similar problems with similar transformations in corn, cotton or canola have not yet been studied. Certainly, government regulators and their academic satellites seem passive and submissive in dealing with important findings reflecting on the safety of GM crops.

Even though the stability and long term stability of transgenic crops is of paramount importance there have been few published studies on the genetic stability and response to varying environments of transgenic crops. A study of transgenic barley showed that GM barley was inferior to conventional barley in a number of genetic backgrounds and
environmental conditions (Horvath et al 2001). Such problems may reflect somaclonal variation or unexpected gene silencing, or they may reflect other unpredicted aspects of genetic modification. In conclusion, there should be a moratorium on the use and distribution of GM crops until the consequences of genetic instability are fully
explored. Government regulators should not be allowed to ignore the consequences of allowing sudden revelations about DNA sequences that crop up unexpectedly in commercial crops sold as unlabelled food to unsuspecting people.

Article first published 08/04/01


  1. Courtail,B,Fenebach,F,Ebehard,S,Rhomer,L,Chiapello,H,Carilleri,C and Lucas,H "Tnt 1 transposition events are induced by in vitro transformation of Aradopsis thaliana, and transposed copies integrated into genes" 2001 Mol Gen Genomics 265,32-42
  2. Demeke,T,Hucl,P,Baga,M,Caswell,K,Leung,N and Chibar,R "Transgene inheritance and silencing in hexaploid spring wheat" 1999 Theor Appl Genet 99,947-53
  3. Horvath,H,Jensen,L,Wong,O,kohl,E,Ullrich,S,Cochran,J,Kannangara,C, and von Wettstein,D "Stability of transgene expression , field performance and recombination breeding of transformed barley lines"2001 Theor Appl Genet 2001,1-11
  4. Palevitz,B "DNA surprise: Monsanto discovers extra sequence in its Roundup Ready soybeans" 2000 The scientist 14,20 (july 24)

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