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Unintended Effects of Genetic Manipulation

Type of Unintended Effect: Physiological (Animals)


Atlantic salmon expressing transgenic growth hormone experienced numerous changes to their cardiorespiratory system.

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

Transgenic expression of growth hormone in coho salmon led to a narrower body, more red muscle mass, and smaller white muscle fibers.

Transgenic coho salmon expressing growth hormone had enlarged heads, reduced viability, and accelerated development of their life cycle.


Transgenic goats engineered to secrete the human protein cholinesterase into their milk produced less milk, with lower fat and lactose levels and unusually high white blood cell counts.


Transgenic pigs expressing bovine growth hormone had lower appetites, enlarged organs, gastric ulcers, and other health problems.

Sheep growth hormone expression was highly variable in transgenic pigs, whose bodies had more protein and water and less fat.

Transgenic pigs with elevated levels of growth hormone were infertile, pre-diabetic, and experienced joint problems.

Transgenic expression of a mouse milk protein impaired mammary development and function in pigs.


Transgenic expression of sheep growth hormone in sheep increased the incidence of reproductive problems and premature death.

Transgenic sheep had unusually high morbidity and expressed a milk-specific protein in their spleen, liver, and other organs.


Tilapia fish engineered for transgenic expression of growth hormone had deformed heads and backs, atrophied gonads, and lower mineral content.

Type of Unintended Effect: Physiological (Plants)


Alfalfa with corn transgenes for anthocyanin (red-purple pigment) production was not visibly altered or changed dependent on different light and temperature conditions.

Plant height and flowering were altered in alfalfa genetically engineered to reduce lignin content.


Apples over-expressing a fruit-ripening enzyme lacked flowers and had malformed stomata and altered composition of cell walls.


Plants producing a biodegradable polyester were smaller, never produced seeds and showed severe changes in metabolism.

Suppression of DHS enzyme in Arabidopsis (a mustard plant) was associated with enlarged leaves, greater root mass, and enhanced seed yield.

Overexpression of phytoene synthase gene in Arabidopsis resulted in delayed germination, increased levels of chlorophyll, and changes in relative levels of carotenoids.

Unintended changes in gene expression were observed in Arabidopsis plants engineered for resistance to the herbicide glufosinate.


Innate Immunity is Affected in Insect-Resistant GM Aspens


Barley expressing a heat-stable enzyme showed highly variable expression of the enzyme, an anomalous distribution of expression in the grain, and dramatically reduced weight of individual grains.

Transgenic barley plants over-expressing a zinc transport protein had smaller seeds and did not accumulate more zinc when grown in zinc-deficient soil.

Difficulties were encountered when trying to express human collagen in barley.

A group of transgenic barley plants expressing the bar selectable marker gene did not produce viable offspring.


Transgenic birch trees expressing an antifungal enzyme from sugarbeets showed increased susceptibility to leaf spot disease in the field.


Canola plants over-expressing a bacterial phytoene synthase gene also had a reduced level of chlorophyll, changed structure of plastids, changed composition of fatty acids, and delayed germination.


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.

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

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


Bt maize has higher lignin content.

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.

Transgene in corn, intended to raise iron availability, also changed levels of other minerals and proteins.

Long-term toxicity of a Roundup herbicide and a Roundup-tolerant genetically modified maize.


Peas engineered to be weevil-resistant elicited immune reactions in mice.


Pineapple plants with transgenes for fungus and herbicide resistance had altered biochemical make-up.


GMO Semi-Dwarf Poplar Trees May Be More Susceptible to Pests


Potatoes with altered sugar metabolism had changed levels of many metabolites, some not thought to be associated with sugar metabolism.

Inulin-storing potatoes had higher alkaloid content and pigs fed on them had reduced daily weight gain.

Potatoes genetically modified to store more starch stored less starch.

Insect-resistant transgenic potatoes had less foliage and altered levels of leaf-glycoalkaloids.

Potatoes with transgene for virus resistance were variably resistant, and some lines without the target gene nevertheless became highly resistant.


Bt rice showed signs of dwarfism and other abnormalities.

Transgenic expression of a disease-resistance gene activated the oxidative-stress response in rice.

Genetically modified (GM) insect-resistant rice and weedy rice hybrids have increased seed production.

Yield differences between insect-resistant Bt rice and non-GM rice.

New GMO Rice Lines in India Are High in Vitamin A Precursor,
But Unfit for Cultivation Due to Low Yield and Lack of Plant Vigor

root nodule bacteria

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


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

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.


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


Sugarcane engineered to reduce polyphenol oxidase (PPO) activity had greater PPO activity, even without the transgene.


Transgenic tobacco with resistance to bleaching herbicides had altered composition of carotenoids.


Tomato plants overexpressing phytoene synthase gene were stunted in growth.

Flavonol-enriched tomatoes had altered levels of at least fifteen other substances.

Suppression of DHS gene in tomatoes was associated with lack of fruiting, altered leaf morphology, higher rate of photosynthesis and other changes.

Transgenic tomatoes altered with a marker gene construct showed significant changes in morphological and physiological characteristics.


Wheat transformed with a high-molecular-weight glutenin gene showed irregular expression of glutenin and changed its expression levels over subsequent generations.

Wheat with transgene for low-molecular-weight glutenin showed anomalies in glutenin production and some plants had reduced levels of other storage proteins.

Spring wheat with scab-resistance transgene was not scab resistant and showed localized death of leaf tissue.

Wheat expressing transgenic glutenin shows reduction in yield, varying production of glutenin, and altered morphology.

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

Pheromone-producing GM wheat does not repel pests in field trials.

herbicide resistance and crop yields

Unintended Effects of Herbicide-Resistance Genes on Crop Yield.

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