The history of controversy behind genetically engineered crops

Since commercialization of the world's first genetically engineered crops in 1995-1996, there has been an ongoing debate globally about the safety and effectiveness of the crops. On Nov. 4, voters in Oregon and Colorado will weigh in on proposed laws that would require foods made with genetically engineered crops and sold in those states to be labeled as genetically engineered.

Here are some facts about genetically modified crops, also called GMOs.

* U.S. corn and soybean farmers have largely embraced genetically modified crops that can tolerate treatments of herbicide and fight off harmful pests, citing enhanced ease of production of critical food, feed and energy crops. GMO crop developers say many scientific studies show the crops are safe. But many farmers, environmentalists and consumer groups say there are also many scientific studies showing GMO crops contribute to health and environmental problems and are not needed to improve global food production. Many critics are specifically concerned about herbicide residue on GMOs.

* Vermont in May became the first U.S. state to pass a mandatory GMO labeling law that can take effect without other states also enacting labeling. The law is set to take effect July 1, 2016, but the grocery manufacturers industry has sued to block it.

* Industry data shows GMO crops planted on 175.2 million hectares (433 million acres) in 2013, with American and Brazilian farmers the dominant users, according to the International Service for the Acquisition of Agri-biotech Applications (ISAAA), a pro-biotech industry organization.

* GMO soybeans, along with corn and cotton, are the most widely planted types of GMO crops. But there are also genetically modified versions of canola, sugarbeet and alfalfa and other crops.

* The most common GMO trait is herbicide-tolerance, which allows farmers to spray over the crops with weed killer without harming the crops. In 2013 U.S. farmers used herbicide-tolerant soybeans on 93 percent of all U.S.-planted soybean acreage. Herbicide-tolerant corn was planted on 85 percent of all U.S. corn acres, according to the U.S. Department of Agriculture.

* A handful of agrichemical and seed companies dominate the global market for GMO crops, including Monsanto Co., DuPont Pioneer, a unit of DuPont, Dow AgroSciences, a unit of Dow Chemical and Syngenta.

* GMO crop are transgenic, meaning their DNA has been spliced with genetic material from other species, or a completely unrelated kind of organism like bacteria or animals, to change the way they function. The genetic trait for herbicide tolerance is derived from the common soil bacterium Agrobacterium sp. strain CP4. Certain GMO crops referred to as "Bt" contain a gene from the soil bacterium Bacillus thuringiensis that produces a protein toxic to specific insects.

(Reporting by Carey Gillam in Kansas City, Mo.; Editing by Meredith Mazzilli)