A lot of people (including me!) are concerned with the possibility of genetically engineered crops spreading their pollen to nearby fields and to wild relatives. I covered some physical and genetic ways to prevent this in Gene flow, IP, and the terminator, but we all know that 100% exclusion of unwanted pollen is impossible (at least for now).

So, what happens when a farmer’s field or wild plant population  is “contaminated” with a transgene? Can they be decontaminated? What about gene flow from non-transgenic crops? Strangely, none of the people concerned with transgenic gene flow seem to be concerned about non-transgenic pollen from modern cultivars, which is a much bigger problem. I use “contaminated” in quotes because nature doesn’t see the distinctions we see. Transgene or not, wild or cultivated, all go into a big mixing pot to be stirred by random mating and natural selection.

If we are to be concerned about transgenes, we must consider the actual effects that those genes might have, and how those genes might act within a population. There are three types of effects an “escaped” transgene could have on wild populations:
1) Some transgenes are expected to have a negative effect on the fitness of wild plants. For example, a gene that dramatically increases the size and number of fruits produced by a plant is desirable from an agricultural perspective, but will likely have detrimental effects on a wild plant, because the plant would have less resources to devote to other needs like herbivore defense and drought tolerance. These types of genes will not persist in a wild population.
2) In contrast, some transgenes are expected to have a positive effect on the fitness of wild plants. For example, a gene for herbivore resistance, such as that found in crops engineered to produce the insecticidal Bt toxin, would help cultivated and non-cultivated plants escape damage from susceptible herbivores. These types of genes will be selected for and thus persist in a wild population.
3) Finally, some transgenes are neutral, expected to have no effect on fitness of wild plants. For example, if a wild plant acquires the gene for glyphosate tolerance, but is never sprayed with this chemical, its fitness will presumably be unaffected. These genes may persist in a wild population at low levels. Since we are talking about one gene, it’s actually very easy to breed it out of a population. We just need to know which plants have the gene and which ones don’t, then keep only seeds from plants that don’t have the gene. This will take one generation if the plants are tested before fertilization, or a few generations if the seeds are tested. Some transgenes are easy to see, while others require a DNA test. For example, plants “contaminated” with a hypothetical transgene encoding for color could be identified by sight and removed. Plants “contaminated” with a transgene that isn’t easy to see can be screened for the suspected gene with PCR, a relatively easy process.
Gene flow from all cultivated plants to wild relatives is a much larger problem than transgenes. Wild populations are generally in genetic equilibrium, such that the population has just the right balance of alleles for each of its genes to ensure maximum survival and the ability to adapt to changes in the environment. When pollen from cultivated plants fertilizes plants in wild populations or landraces, only 1/2 of the genes in the resulting plants are wild. If enough of the plants are fertilized with cultivated pollen, genetic diversity in future generations can be seriously decreased. With a decrease in diversity, the population is less able to survive changes in the environment. Rice in Asia has been severely affected by non-transgenic gene flow, so much so that it is difficult if not impossible to find wild rice plants that do not contain some genes from modern cultivars.
A specific example of confusion about the problem of gene flow can be found in the movie “The World According to Monsanto” which can be found on YouTube. Starting at the end of part 6 of 8 and through half of part 7 of 8, the movie discusses contamination of maize landraces in mexico with transgenes. They say that farmer’s plants are becoming “monsterous” due to transgenes. They say that “transgenes will insert themselves into different places in the genomes of the farmer’s corn”, which is less than scientifically accurate, to say the least.
Natural transposons found in many organisms can “jump”, inserting themselves into new places in the genome, but transgenes don’t have this ability any more than normal genes do (they don’t). It’s hard to say what is causing the “monstrosities” but I’d wager it has a lot more to do with the combination of highly different genomes that haven’t had contact for decades or possibly even hundreds of years. I don’t know what else to say, except that the interpretation of gene flow presented in the movie is overly simplistic and ignores a lot of the bigger issues associated with loss of biodiversity. Blaming genetic engineering is easy, but doesn’t help solve any problems.
Note – I’m only discussing the gene flow part of the movie in this post, so please hold your horses if you have comments on the rest of it. If you have particular parts of the movie you’d like to discuss, let me know in a comment.

Written by Anastasia Bodnar

Anastasia Bodnar is a science communicator and science policy expert with a PhD in plant genetics and sustainable agriculture from Iowa State University. Anastasia has had various risk analysis roles in US government and military service. She serves as BFI's Director of Policy and as Co-Executive Editor of the Biofortified Blog.


  1. Hello Anastasia,
    Concerning the gene flow between maize plants the risk is quite limited


    In the movie “the world according to Monsanto there are many wrong statements made by the journalist. The link between some Arabidopsis that overexpress a transcription factor from MAD box family (Agamous like 21, we can see it on the screen of the scientist) and these mishape maize presented by a activist is pure manipulation and lie. There is no scientific link between both. It could maybe be some kind of developpemental defects resulting from insect dommage in the meristem or fungi or whatever. Your explaination could also be a possibilty.
    Concerning the other “mistakes” present in the movie for people who understand french you can read that.
    There are others.
    All the best,

  2. I hadn’t finished watching the film, so I checked out the clip in question. This “Monstrous Maize” is a trait that turns up naturally in some varieties. Out in the field this summer, several of the diverse varieties of maize that we were growing produced multiple ears. I’d sure like to see the evidence that a Bt gene would all of a sudden cause something quite different to happen like multiple ears. Guilt by association.

    The floral mutants shown in the clip are also very misleading. Changes in floral homeotic genes can lead to the alteration of many parts of the flower, conversion of some flower parts into one another, like sepals into petals, or petals into anthers, etc. What they are showing is the results of a genetic screen by insertion. Little different from a T-DNA library, or a deletion screen – it proves that if you can change the expression of genes in a plant, you can change the way it looks! I guess bothering to understand the genetics involved doesn’t make a good film intended to scare people.

    This film needs to be panned over by a team of people who are knowledgeable about the subject. I’m already thinking about how best to respond to it.

  3. Thanks for the precision about this phenotype that can appears naturally. Is there publication that would describe this somewhere? By the way there is a mistake in the second link I pasted in the first message: everything after the “?” should be remove otherwise it doesn’t work. I agree with you there are to many things to rectify in this movie for only one person and several specialists should work on this.
    A guy started a blog with a funny title (“the world according to Mme Robin”) in which he address some aspect discussed on her blog and movie but he didn’t continue, that’s lot of work.

  4. Mutants of Maize is an excellent book that has beautiful pictures of hundreds of interesting phenotypes (none of which are caused by genetic engineering!).–eqSKUdatarq=29

    I’ll stop by the school library soon and see if the mutation is in the book. If it is, I’ll scan and post it.

    Oh, and on gene flow, I know the risk is low (as I discussed in the post Gene Flow, IP and the Terminator), but I think it is something we should consider anyway. Although, again, I think the hoopla over transgenes is silly when there are so many other genes to worry about.

  5. You mean you don’t have Mutants of Maize at home on your bookshelf? What kind of corn geneticist ARE you? 🙂

    I went through my copy of the book, and I didn’t find anything – the exact cause is unknown, except we know that it shows up in a few varieties. One inbred line that I’m trying to cross to my own stocks, CML 154Q, had multiple ears at each node. There’s no transgenes in this inbred line, nor the others.
    Here are a couple links to some descriptions of the phenomenon:

  6. I find it very odd that there are journalists out there that want to cover a topic related to science, but don’t interview anyone that actually knows anything about the topic. A farmer in Mexico doesn’t know about multiple ear syndrome, and Ignacio Chapela isn’t even a plant biologist.

    I know of a wiki system that could be easily set up as a place to arrange an organized review and response to this film and others. We can even make it passworded.

  7. In the current state of the art, the need to contain transgenes is questionable at best. In the few instances where traits can outcross between crops, or from crops to weeds, none of the traits pose any risk to humans, or to the environment.

    Though containment currently serves only political/economic/culinary interests, it’s been proven feasible.

    In the US, there are no detectable levels of StarLink maize, anywhere. GM rice has disappeared from US stocks.

    Furthermore, after Chapela’s work was exposed as a hoax, a comprehensive study of Mexico’s maize has found no GM transgenes.

    As to Inoculated mind’s remark about journalists who “don’t interview anyone who actually knows anything about the topic”, I would point out that modern journalists seek “independent” sources.

    What source could possibly be *more* “independent” than someone who knows nothing of the field? As poster children for the “independent” sources, I would recommend Vandana Shiva and Jeffrey Smith–respectively, a physicist, and a dance-class teacher who also does yogic flying. These two are widely considered to be “independent experts” on GM crops.

  8. Andrew, I completely agree with your last paragraph. Who the heck are these people to be discussing things they know nothing about? You can add Claire Hope Cummings to the list – she’s a lawyer who attempts to write about the science of GE, instead of the the very important issues of IP and regulation that she’s actually qualified to write about! I might consider economics, ethics, etc on my blog, but I certainly don’t think I’m qualified to write a book about them!

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