What Are Genetically Modified Organisms?

Definition & Examples of Genetically Modified Organisms

Scientist pipetting liquid into test tube in laboratory

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Table of Contents
Table of Contents

Genetically modified organisms, or GMOs, are plants and animals with altered genetic makeup. They have been edited in a laboratory to incorporate genes from other organisms to achieve new characteristics like chemical resistance or accelerated growing time.

GMOs are widely used in United States agriculture.

Learn how this process differs from other breeding techniques and whether it is safe.

What Are Genetically Modified Organisms?

Genetically modified organisms are plants and animals that have been altered in a laboratory to have new genetic makeup. Scientists incorporate genes from other organisms to achieve new characteristics that are not inherent to the plants and animals being modified.

When scientists use genetic engineering to alter the genes of an organism, they're generally seeking to add a trait they view as beneficial, usually for production purposes. Genetic engineering is often done to achieve a trait not typically held by an organism, such as longer shelf life, disease resistance, or different colors or flavors.

The dangers and benefits of GMOs are widely debated, but genetic modification is allowed in conventional farming in the U.S.

Foods that are certified organic cannot contain genetically modified ingredients.

Alternate names: genetically engineered crops, GE crops, genetically engineered organisms, bioengineered crops, GM foods

Acronym: GMO, GM, GE

How Genetically Modified Organisms Work

Farmers have traditionally bred both plants and animals to increase desirable characteristics. Traditional methods for doing this include:

  • Choosing seeds from the healthiest or fastest-growing plants as the sources for the next year's crop
  • Grafting branches from one tree onto another to create new varieties of fruit
  • Breeding animals for size or output, such as milk or egg production

Increased knowledge of plant and animal genetics led to the practice becoming more sophisticated, allowing farmers and scientists to breed for more selective traits. They also began creating new crop hybrids in laboratories and applying chemicals and radiation in an effort to induce desired changes in plants' genetic makeup.

These efforts have led to a variety of new crops, such as rice cultivars that are resistant to drought or wheat cultivars that have a much higher yield.

GMOs take these efforts to yet another level and go beyond naturally occurring traits that can be achieved through selective breeding. Instead of inducing mutations that deliver desired characteristics, GMO scientists directly edit the genetic code of plants and animals by inserting genes that carry the characteristics being sought.

The genes being introduced into one species can come from a completely unrelated species, depending on the traits that scientists are trying to create.

Types of Genetically Modified Organisms

A well-known example of a GMO food is Roundup Ready ​corn, a variety of corn created by Monsanto Company that's resistant to the herbicide glyphosate. This GMO-bred glyphosate resistance stems from the addition of a bacterium gene and enables farmers to use more of the herbicide, also manufactured by Monsanto, on their fields containing the corn.

Monsanto also has created Roundup Ready soy, alfalfa, canola, cotton, and sorghum. In addition, the company has genetically modified corn, soybeans, and cotton in order to make those crops more resistant to insects.​

Monsanto was the subject of several liability lawsuits regarding Roundup products. In 2018, the company was acquired by Beyer, and in 2020 Beyer reached a settlement regarding Roundup product liability litigation. 

Other companies are developing genetically modified animals. For example, AquaBounty Technologies created AquAdvantage salmon, a genetically modified Atlantic salmon approved by the U.S. Food and Drug Administration (FDA). It incorporates genes from other fish, including the Chinook salmon, that enable it to grow twice as fast as nongenetically modified Atlantic salmon.

Prevalence of GMOs

Two common types of genetically engineered crops are insect-resistant (Bt) crops and herbicide-tolerant (HT) crops. Bt crops contain genes from Bacillus thuringiensis (Bt) bacteria and produce insecticidal proteins. HT crops are tolerant to herbicides that farmers use to control weeds.

The number of acres growing Bt crops and HT crops in the United States has increased dramatically since the mid-1990s. HT cotton accounted for 10% of planted acres in 1997 but increased to 95% by 2019, while Bt cotton increased from 15% of cotton acreage in 1997 to 89% in 2020.

"Stacked" GMOs have both HT and Bt traits. The use of stacked seeds has increased in the U.S. as well. Stacked corn accounted for 79% of planted corn acres in the U.S. in 2020.

Other common GMO crops in the United States include:

  • HT corn
  • Bt corn
  • HT soybeans

These crops are the foundation for ingredients such as oils, sweeteners, and more that are used in many of the products sold on store shelves. Other GMO crops approved in the U.S. include:

  • Canola
  • Alfalfa
  • Sugar beets
  • Papaya
  • Squash
  • Apples
  • Potatoes
  • Salmon

Criticisms of Genetically Modified Organisms

The debate about genetically modified organisms is ongoing, both culturally and politically.

Proponents say that the uses of GMOs improve the food supply by increasing or accelerating food production. Opponents say that the risks to both humans and the environment outweigh these benefits.


The World Health Organization (WHO) states that GMOs currently available are no more likely to cause health problems than traditional foods, but it also states that foods need to be assessed on a case-by-case basis.

In the U.S., GMOs are regulated by the FDA, the USDA, and the Environmental Protection Agency (EPA). The main concerns of GMO critics are:

  • Allergic reactions
  • Possibility of transferred genes in foods entering human cells and having a negative effect
  • Outcrossing, or genes from GMOs find their way into conventional crops

According to WHO, no allergic effects have been found in GMOs on the market, and the possibility of gene transfers and outcrossing are low, though precautions are encouraged.

Other concerns about genetically modified crops include the farming practices that their use encourages. For example, studies have found that the use of glyphosate has increased significantly since the introduction of Roundup Ready crops.

There are lingering questions in the scientific and environmental community about the impact on both human and environmental health as a result of this increase. Glyphosate is classified as a probably human carcinogen .

Environmental Impact

Another controversy surrounding GMOs involves their impact on the environment, such as the impact of Bt crops on non-target species.

For example, bees are not considered to be a pest, but Bt crops still possibly cause harm to bee populations, which in turn impact the pollination of various ecosystems and crops. Butterflies and birds are also cited as non-target species that could be affected.

Additionally, pests or plants that are impacted are likely to eventually become resistant to the negative effects Bt crops might have on them, leading to an endless cycle of crops being altered further, followed again by further resistance from pests. This has been shown to happen with the growth of glyphosate-resistant weeds as a result of glyphosate being overused after the introduction of Roundup Ready crops.

The impact Bt and HT crops can have on organisms and microorganisms necessary for healthy soil also is a concern.

Key Takeaways

  • Genetically modified organisms, or GMOs, are plants and animals with altered genetic makeup.
  • They have been edited in a laboratory to incorporate genes from other organisms to achieve new characteristics like chemical resistance or accelerated growing time.
  • GMOs are used widely in the United States, including GM corn, cotton, soybeans, and more.
  • The World Health Organization states that GMOs are currently thought to be safe for humans, though their broader health and environmental impacts are still being investigated.