Potassium deficiency symptoms on a tomato leaf

Advocates claim unintended and possibly harmful changes in plants caused by genetic modification methods, including the new gene editing techniques, can be “bred out”. But this is often not true, says Dr Doug Gurian-Sherman

Advocates of old-style GM crops as well as the new gene-edited crops often tell us we shouldn’t worry about the unintended effects of the genetic engineering process because they will be identified and can be “bred out” by backcrossing the GM crop with non-GM plants prior to commercialisation.[1] We’re also told that so-called gene editing techniques can avoid such harmful effects.

But this is often not true, according to biotech expert Dr Doug Gurian-Sherman, a research consultant with Minneapolis-based Strategic Expansion and Trainings, LLC, which focuses on supporting ecologically based sustainable agriculture.

Dr Gurian-Sherman said, “There are several types of unintended effects of the genetic engineering process. Some are caused by disruptive insertion of fragments (or even whole copies) of the transgenes or vector sequences into various places in the genome. Some are caused by mutations of various kinds due to tissue culture. These are often what molecular biologists and geneticists call ‘unlinked’ (physically separated in the genome from the gene targeted for modification). These can indeed often be removed by backcrossing to a non-engineered variety.

“Even unintended effects from a bad insertion site or position effects (the influence of the location of a gene on its activity) may be remedied by a new version of the engineered plant (a so-called new "transformation event") – provided that the problem is recognized.

“But other sources of unintended effects are ‘linked’ physically (nearby in the DNA) or functionally to the introduced engineered gene and so cannot be removed by backcrossing. These include complex and unpredicted interactions between the engineered gene (or its RNA and/or protein expression products) and other genes. Such effects may include altering the expression of a plant toxin, or causing the accumulation of a product in a metabolic pathway that normally does not accumulate it or where it is present in only very tiny amounts. These interactions can also adversely impact the performance of the crop in unanticipated ways that are not revealed in limited field trials. There are a number of cases in the science literature that seem to be unintended effects of these types, even though few research studies are designed to discover them.

“It seems likely that some of the unintended effects of the genetic engineering process seen in “Pandora’s Potatoes”, the GM potatoes engineered by Dr Caius Rommens, are of this type.

“And because potatoes are normally vegetatively propagated (cloned) and are not bred by cross-pollination, it is difficult to remove any unintended effects, whatever their origin, by backcrossing.”

Gene editing won’t solve the problem

Asked if the new gene editing techniques will solve all these problems, Dr Gurian-Sherman said they would not: “The harmful unintended effects due to interaction of the intended alteration at a genomic, RNA or protein level remain a potential problem with gene editing applications, even if genetic engineers eventually succeed in addressing the other types of unintended effects seen with the older GMOs.”

In addition to these points, it is unlikely that genetic engineers will spot many types of unintended effects that could make the resulting GM crops toxic or allergenic, or unexpectedly vulnerable to environmental stresses such as bad weather, pests, and disease. This is because most of what they do when selecting out the “undesirable” plants is check that the plant is growing well and looks healthy. Such a superficial check cannot identify mutations or changed biochemistry that can lead to these serious problems.

Dr Gurian-Sherman said, “There are some recommendations (in the US, for example) to assay for a few known crop toxins, and a few tests for allergenicity, but these do not include the broad spectrum of potential harmful unintended effects.”

In short, based on these points, we cannot assume that unintended effects in GM crops, including gene-edited crops, will be safely “bred out” before commercialisation.


1. This applies to crops such as maize and soy, which are propagated by cross-pollination, but not to crops such as potatoes, which are generally vegetatively propagated (cloned). Many potatoes can be bred, but it is often challenging to do so while maintaining the desired characteristics of the original variety.