They are "linked to toxic and allergic reactions, sick, sterile,
and dead livestock, and damage to virtually every organ studied in lab animals.
...Crops such as Bt cotton produce pesticides inside the plant. ... Farmers in India, who let their sheep graze on Bt cotton plants after the harvest, saw thousands of sheep die!" - responsibleTechnology.org.
"Currently commercialized GM crops in the U.S. include soy (94%), cotton (90%), canola (90%),
sugar beets (95%), corn (88%), Hawaiian papaya (more than 50%), zucchini and yellow squash (over 24,000 acres).
Products derived from the above, ...soy protein, soy lecithin, cornstarch, corn syrup and high fructose corn syrup among others. ...First introduced into the food supply in the mid-1990s, GMOs are now present in the vast majority of processed foods in the US. While they are banned as food ingredients in Europe and elsewhere, the FDA does not even require the labeling of GMOs in food ingredient lists." - responsibleTechnology.org.
*GMO seeds can withstand Glyphosate, the herbicide in RoundUp.
*Glyphosate is a antibiotic.
*All antibiotics increase the incidence of breast cancer and probably other cancers too.
*Also, exposure to glyphosate changes the human microbiome - gut bacteria. full text