A genetically modified crop is a plant whose DNA has been altered in a laboratory to introduce a specific trait it wouldn’t acquire through traditional breeding. That trait might be resistance to insects, tolerance to a particular herbicide, or improved nutritional content. More than 90 percent of U.S. corn, cotton, and soybeans are now grown from genetically modified seeds, making these crops a routine part of the food supply even if they remain a topic of public debate.
How Scientists Modify a Crop’s DNA
The most common approach, called transgenesis, involves inserting a gene from a different species into a plant’s genome. A well-known example: taking a gene from a soil bacterium and placing it into corn so the corn produces its own insect-killing protein. The inserted gene becomes part of the plant’s DNA and is passed down to future generations of seed, just like any other gene.
Public concern about mixing genes across species that would never cross-pollinate naturally led to two alternative approaches called cisgenesis and intragenesis. Both restrict modifications to genes from the same species or from close relatives that could theoretically cross-breed. The distinction matters for regulation in some countries, but neither technique has been adopted as widely as transgenesis.
A newer method, CRISPR gene editing, doesn’t necessarily insert any foreign DNA at all. Instead, it precisely alters genes the plant already has. The USDA has determined that some CRISPR-edited plants are equivalent to conventionally bred varieties and don’t require the same regulatory oversight as traditional GMOs. The European Union takes a stricter stance, classifying all gene-edited plants as genetically modified regardless of whether foreign DNA is present.
Insect Resistance: How Bt Crops Work
One of the most widespread modifications gives crops the ability to defend themselves against specific insect pests. Scientists accomplish this by inserting genes from a naturally occurring soil bacterium called Bacillus thuringiensis (Bt). These genes instruct the plant to produce proteins that are toxic to certain insects but harmless to mammals.
The proteins function as stomach poisons. When a target insect chews on the plant and swallows the protein, enzymes in its digestive system activate it. The activated protein binds to receptors in the insect’s gut lining and punches holes in the cell membranes, forming tiny channels that disrupt the cells. The insect stops feeding and dies. Because the protein requires specific receptors found only in certain insect guts, it doesn’t affect humans, livestock, or most beneficial insects.
Different Bt proteins target different pests. In corn, one protein controls the European corn borer, while another targets the Western corn rootworm, a destructive soil-dwelling larva. In cotton, Bt proteins protect against the tobacco budworm and cotton bollworm. As some pest populations have developed partial resistance to earlier proteins, newer varieties have been introduced, and many modern seeds contain two or more Bt proteins stacked together for broader protection.
Herbicide Tolerance: Surviving Weedkiller
The other dominant modification makes crops tolerant to glyphosate, the active ingredient in Roundup and similar herbicides. In an unmodified plant, glyphosate shuts down an enzyme essential for producing certain amino acids. Without those amino acids, the plant can’t make proteins and dies within days.
Herbicide-tolerant crops carry a gene from a soil bacterium that produces a slightly different version of that same enzyme. The modified enzyme does the same job for the plant but has a subtle structural difference: a single amino acid change in its active site prevents glyphosate from locking onto it in its usual inhibitory position. The herbicide still enters the plant, but it can’t block the enzyme’s function, so the crop survives while surrounding weeds die.
This system simplifies weed management dramatically. Farmers can spray an entire field after the crop has emerged, killing weeds without damaging the crop. In 2025, 96 percent of U.S. soybean acres, 93 percent of upland cotton acres, and 92 percent of corn acres were planted with herbicide-tolerant varieties.
Nutritional Enhancement: The Golden Rice Example
Not all modifications target farming efficiency. Golden Rice was engineered to address vitamin A deficiency, which affects an estimated 250 million schoolchildren worldwide and can cause blindness and weakened immunity. Ordinary white rice contains almost no beta-carotene, the pigment the body converts into vitamin A. Golden Rice contains genes that activate beta-carotene production in the grain, giving the rice its distinctive yellow-orange color.
The first version produced only about 0.8 micrograms of beta-carotene per gram of dry rice. The second generation, which uses a gene from maize instead of daffodil, produces up to 35 micrograms per gram. A clinical trial published in the American Journal of Clinical Nutrition found that a 100-gram serving of uncooked Golden Rice could supply 80 to 100 percent of an adult’s estimated average requirement for vitamin A. For children ages four to eight in rice-eating regions, roughly 50 grams of uncooked rice could cover more than 90 percent of their daily need.
Global Adoption and Key Crops
Genetically modified crops are grown on a massive scale. As of 2018, 26 countries planted 191.7 million hectares of biotech crops, up from essentially zero in the mid-1990s. Five countries account for 91 percent of that total: the United States, Brazil, Argentina, Canada, and India.
The United States leads in both acreage and variety. Most commercial GM seeds now contain “stacked” traits, combining insect resistance and herbicide tolerance in a single seed. In 2025, about 87 percent of U.S. cotton acres and 84 percent of corn acres were planted with stacked varieties. Soybeans, canola, sugar beets, alfalfa, and papaya are also widely grown in modified form. Outside the U.S., India has adopted Bt cotton extensively, and Brazil grows large quantities of GM soybeans and corn.
Impact on Pesticide Use
One of the central promises of GM crops was reducing chemical pesticide applications. Over the 24-year period from 1996 to 2020, widespread use of insect-resistant and herbicide-tolerant seeds reduced global pesticide application by 748.6 million kilograms of active ingredient, a 7.2 percent decrease. The environmental impact, measured by a composite indicator that accounts for toxicity and persistence in the environment, dropped by a larger 17.3 percent, because the chemicals eliminated tended to be more harmful than those that replaced them.
Insect-resistant cotton delivered the single biggest change: a savings of 339 million kilograms of insecticide active ingredient, with the associated environmental impact falling by roughly a third. The picture for herbicide-tolerant crops is more nuanced. While they initially reduced herbicide use, the emergence of glyphosate-resistant weeds in some regions has led farmers to apply additional herbicides, partially offsetting early gains.
Safety and Regulatory Oversight
No direct safety hazard from consuming genetically modified foods has been documented since commercial GMOs entered the market in the mid-1990s. Governments have established some of the strictest testing requirements in food regulation to evaluate each new GM variety before it reaches consumers.
In the United States, three federal agencies share oversight. The USDA’s Animal and Plant Health Inspection Service evaluates whether a modified plant could become a plant pest or pose risks during field trials and transport. The FDA’s Center for Food Safety and Applied Nutrition reviews the safety of food derived from GM plants through a consultation process. The EPA regulates any pesticidal substances the plant produces, such as Bt proteins, assessing risks to human health and the environment. A new GM crop typically goes through all three agencies before reaching the market, a process that can take years and cost tens of millions of dollars.
Regulatory approaches vary globally. The EU requires mandatory labeling of foods containing more than 0.9 percent GM ingredients and applies its precautionary framework to gene-edited crops as well. In the U.S., a national disclosure standard requires food manufacturers to indicate the presence of bioengineered ingredients, though the format (text, symbol, or QR code) is more flexible than European labels.