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Unintended Effects of Genetic Manipulation

Jump below to specific type of unintended effect:
Type of Unintended Effect: environmental (animals)


Coho salmon engineered for transgenic expression of growth hormone were more aggressive predators in simulated natural environments.

Genetically modified atlantic salmon/brown trout hybrids have unexpected ecological effects.

Type of Unintended Effect: environmental (plants)


Innate immunity is affected in insect-resistant GM aspens.

Leaf litter from insect-resistant transgenic trees causes changes in aquatic insect community composition.

Insects feed less on insect-resistant aspen leaves, but the trees don’t grow larger than unmodified aspens.


Spread of herbicide-resistance from genetically modified creeping bentgrass into the wild.


Experimental crosspollination between transgenic herbicide-resistant canola and wild field mustard led to highly fertile, herbicide-resistant wild field mustard.

Transgenes that have escaped from glyphosate-resistant canola can persist in the wild.

Conventional, certified canola seedlots were contaminated with genetically engineered seeds.

Herbicide-resistant canola volunteers still detected after ten years of stringent control.

Fewer wild bees were observed in glyphosate-resistant canola fields.


Bt cotton showed decreased ability to kill cotton bollworm larvae during flower development and flowering.

Bt cotton had altered protein metabolism and produced less insecticidal toxin in leaves when subjected to high temperatures during boll formation.

Increased resistance to Bt toxin is found in some populations of cotton bollworm (Helicoverpa zea).

Cotton plants and seeds expressing Bt toxin were found in non-Bt refuges.

Traditional Non-GMO Cotton Can Yield Economic Benefits Similar to GMO Cotton on Non-Irrigated Small Farms in India


Root nodule bacteria with Bt transgene tended to displace non-manipulated bacteria in legume root nodules.


Monarch butterfly larvae exposed to anthers from Bt maize ate less and gained less weight.

Byproducts from Bt maize enter streams, and in feeding experiments affected stream insects.

Bt maize had changed lipid composition in stems; also, lipid composition in soil was altered, and soil respiration was reduced.

Western corn rootworms were found feeding on volunteer corn plants expressing a Bt toxin specific to that pest.

Western corn rootworm not killed by Bt corn in Iowa.

Perspective matters: Bias and conflict of interest in studies about genetically modified organisms.


Genes escaped from cultivated GM rice to its weedy and wild relatives.


Herbicide-resistant soybean plants were shorter, with less chlorophyll, lower weight, and increased susceptibility to stem-splitting at high temperatures.

sugar beet

Glyphosate-resistant sugar beet production alters population densities of some arthropods, significantly reducing the number of bees and butterflies in beet fields.

sugar cane

Lectin transgene for stemborer resistance alters growth of sugarcane.


Wild sunflowers with transgene for Bt toxin produced more seeds than normal wild sunflowers.


GM wheat outcrosses more often than unmodified wheat of the same varieties

RNAi interference

Potential unintended effects of RNAi-based insecticidal crops

insect resistance

Western corn rootworm not killed by Bt corn in Iowa

Increasing resistance of pests to genetically modified, insect-resistant Bt crops

weed resistance

Increased planting of glyphosate-resistant crops and application of glyphosate causes increase in glyphosate-resistant weed species.

Type of Unintended Effect: environmental (microorganisms)


Why GM bacteria haven’t succeeded in the real world: It’s the context, not only the genes

Type of Unintended Effect: environmental (social/economic)

economics of GMO crops

Traditional Non-GMO Cotton Can Yield Economic Benefits Similar to GMO Cotton on Non-Irrigated Small Farms in India

Adoption of GM Cotton Slowing in West Africa Due to Concerns About Inferior Qualities of Crop

farmer stress

GM cotton and suicide rates.

scientific bias

Perspective matters: Bias and conflict of interest in studies about genetically modified organisms.

seed contamination

International shipments of food and feed are increasingly contaminated with genetically modified (GM) products.

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