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Unintended Effects of Genetic Manipulation

Commercialized Product


Experimental cross-pollination 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 were 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).

Glyphosate-resistant cotton that is sprayed with glyphosate showed abnormal reproductive development.

Fruiting morphology was altered when glyphosate-resistant cotton was sprayed with glyphosate.

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

Insect-resistant, transgenic cotton was more susceptible to fungal disease than its parent line.

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


Bt maize has higher lignin content.

Atlantic salmon fed Bt corn had altered enzyme activity in liver and intestine as well as altered proportions and numbers of different white blood cells.

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 varieties matured more slowly and had on average lower grain yield and higher grain moisture content than conventional varieties.

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.

The transgenic sequences of some Bt maize plants have changed since they were approved.

Western corn rootworm not killed by Bt corn in Iowa.

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

GM Maize Differs from Non-GM Maize at Molecular Level In Unintended Ways, Including in Response to Drought Stress


Glyphosate-resistant GM soybeans differ compositionally from non-GM soybeans and contain high residues of the herbicide glyphosate.

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

Diet containing glyphosate-resistant soybeans affected the nuclei of liver cells in mice.

Glyphosate-resistant soybeans had lower yields.

Root colonization of glyphosate-resistant soybeans by pathogenic Fusarium fungi increased with glyphosate application.

Glyphosate-resistant soybeans have altered root nodules when sprayed with glyphosate.

Transgenic DNA from glyphosate-resistant soybeans was detected in the intestinal flora of humans.


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

Glyphosate-resistant sugar beets became more susceptible to root rot when sprayed with glyphosate.

Commercialized Products in General

Food and feed contamination

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

Herbicide-resistant crops

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

Insect-resistant crops

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

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