General Mills announced its iconic cereal brand Cheerios will no longer contain ingredients with genetically modified organisms (GMOs). What exactly are GMOs, and where else are they found? USA TODAY Network examines these and a few other questions you may have.

MORE: Cheerios drops genetically modified ingredients

What are GMOs?

GMOs are plants or animals whose cells have been inserted with a gene from an unrelated species in order to take on specific characteristics. For example, plants might be genetically engineered to develop a resistance against insects or to increase nutrients. GMOs have been part of our food for the past 20 years. No genetically engineered animals have been approved for sale for human consumption in the United States.

Why are some people concerned about GMOs?

Critics say there are potential health effects (see next question) and environmental concerns surrounding GMOs. One of the supposed benefits of GMOs is that they should result in less herbicide spraying, since some plants have been modified to be herbicide resistant. However, over-reliance on these crops has led to the emergence of "super weeds" that are also more resistant to herbicides, requiring increased spraying, according to a University of Washington study.

Are genetically modified foods safe to eat?

GMO critics say genetically engineering a food could affect its nutritional value or create allergens or toxins in the food, although these claims are disputed by federal regulators, including the Food and Drug Administration.

Three agencies -- the FDA, U.S. Department of Agriculture and the Environmental Protection Agency -- regulate GMOs for safety. According to the FDA, genetically modified foods are regulated the same as any other foods.

Which foods contain GMOs?

More than 40 types of plants have been genetically modified worldwide. A much smaller number are commercially grown. The most common genetically modified plants are corn, canola, soybean and cotton. Others include papayas, chrysanthemums, poplars, spruce, according to the U.S. Department of Agriculture. GMOs have also been used in tobacco, rice, cranberries, raspberries and walnuts, but these are not grown in the United States for human consumption.

How can I tell if my food contains GMOs?

Currently, food manufacturers are not required to label whether their products contain GMOs. The FDA only requires that labels are "truthful and not misleading." FDA is considering two citizen petitions it has received asking the agency to require GMO labeling.

GMOs, however, are prohibited in organic products. "This means an organic farmer can't plant GMO seeds, an organic cow can't eat GMO alfalfa or corn, and an organic soup producer can't use any GMO ingredients," according to the USDA. Additionally, organizations, like the Non-GMO Project, list products verified to be GMO-free. You can also download the Non-GMO Shopping Guide app.

Some companies are moving away from GMOs. Fast-food chain Chipotle has committed to removing GMO ingredients from its menu. Also, Whole Foods Market said by 2018 it will label all GMO products at its U.S. and Canadian stores.

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Elizabeth Weise contributed to this story.

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