What Is Genetic Modification?

GMO tomato
The first genetically engineered food on the market was the Flavr Savr tomato. (Image credit: Shutterstock)

Genetic modification is the process of altering the genetic makeup of an organism. This has been done indirectly for thousands of years by controlled, or selective, breeding of plants and animals. Modern biotechnology has made it easier and faster to target a specific gene for more-precise alteration of the organism through genetic engineering.

The terms "modified" and "engineered" are often used interchangeably in the context of labeling genetically modified, or "GMO," foods. In the field of biotechnology, GMO stands for genetically modified organism, while in the food industry, the term refers exclusively to food that has been purposefully engineered and not selectively bred organisms. This discrepancy leads to confusion among consumers, and so the U.S. Food and Drug Administration (FDA) prefers the term genetically engineered (GE) for food.

A brief history of genetic modification

Genetic modification dates back to ancient times, when humans influenced genetics by selectively breeding organisms, according to an article by Gabriel Rangel, a public health scientist at Harvard University. When repeated over several generations, this process leads to dramatic changes in the species.

Dogs were likely the first animals to be purposefully genetically modified, with the beginnings of that effort dating back about 32,000 years, according to Rangel. Wild wolves joined our hunter-gatherer ancestors in East Asia, where the canines were domesticated and bred to have increased docility. Over thousands of years, people bred dogs with different desired personality and physical traits, eventually leading to the wide variety of dogs we see today.

The earliest known genetically modified plant is wheat. This valuable crop is thought to have originated in the Middle East and northern Africa in the area known as the Fertile Crescent, according to a 2015 article published in the Journal of Traditional and Complementary Medicine. Ancient farmers selectively bred wheat grasses beginning around 9000 B.C. to create domesticated varieties with larger grains and hardier seeds. By 8000 B.C., the cultivation of domesticated wheat had spread across Europe and Asia. The continued selective breeding of wheat resulted in the thousands of varieties that are grown today.

Corn has also experienced some of the most dramatic genetic changes over the past few thousand years. The staple crop was derived from a plant known as teosinte, a wild grass with tiny ears that bore only a few kernels. Over time, farmers selectively bred the teosinte grasses to create corn with large ears bursting with kernels.

Beyond those crops, much of the produce we eat today — including bananas, apples and tomatoes — has undergone several generations of selective breeding, according to Rangel.

The technology that specifically cuts and transfers a piece of recombinant DNA (rDNA) from one organism to another was developed in 1973 by Herbert Boyer and Stanley Cohen, researchers at the University of California, San Francisco, and Stanford University, respectively. The pair transferred a piece of DNA from one strain of bacteria to another, enabling antibiotic resistance in the modified bacteria. The following year, two American molecular biologists, Beatrice Mintz and Rudolf Jaenisch, introduced foreign genetic material into mouse embryos in the first experiment to genetically modify animals using genetic engineering techniques.

Researchers were also modifying bacteria to be used as medications. In 1982, human insulin was synthesized from genetically engineered E. coli bacteria, becoming the first genetically engineered human medication approved by the FDA, according to Rangel.

Corn as we know it today was derived from teosinte, a wild grass with small ears and just a few kernels. (Image credit: Shutterstock)

Genetically modified food

There are four primary methods of genetically modifying crops, according to The Ohio State University:

  • Selective breeding: Two strains of plants are introduced and bred to produce offspring with specific features. Between 10,000 and 300,000 genes can be affected. This is the oldest method of genetic modification, and is typically not included in the GMO food category.
  • Mutagenesis: Plant seeds are purposely exposed to chemicals or radiation in order to mutate the organisms. The offspring with the desired traits are kept and further bred. Mutagenesis is also not typically included in the GMO food category.
  • RNA interference: Individual undesirable genes in plants are inactivated in order to remove any undesired traits.
  • Transgenics: A gene is taken from one species and implanted in another in order to introduce a desirable trait.

The last two methods listed are considered types of genetic engineering. Today, certain crops have undergone genetic engineering to improve crop yield, resistance to insect damage and immunity to plant diseases, as well as to introduce increased nutritional value, according to the FDA. In the market, these are called genetically modified, or GMO crops.

"GMO crops presented a lot of promise in solving agricultural issues," said Nitya Jacob, crop scientist at Oxford College of Emory University in Georgia.

The first genetically engineered crop approved for cultivation in the U.S. was the Flavr Savr tomato in 1994. (In order to be grown in the U.S., genetically modified foods must be accepted by both the Environmental Protection Agency (EPA) and the FDA.) The new tomato had a longer shelf-life thanks to the deactivation of the gene that causes tomatoes to start becoming squishy as soon as they're picked. The tomato was also promised to have enhanced flavor, according to the University of California Division of Agriculture and Natural Resources.

Today, cotton, corn and soybeans are the most common crops grown in the U.S. Nearly 93 percent of soybeans and 88 percent of corn crops are genetically modified, according to the FDA. Many GMO crops, such as modified cotton, have been engineered to be resistant to insects, significantly reducing the need for pesticides that could contaminate groundwater and the surrounding environment, according to the U.S. Department of Agriculture (USDA).

In recent years, the widespread cultivation of GMO crops has become increasingly controversial.

"One concern is the impact of GMOs on the environment," Jacob said. "For example, pollen from GMO crops can drift to fields of non-GMO crops as well as into weed populations, which can lead to non-GMOs acquiring GMO characteristics due to cross-pollination."

A handful of large biotechnology companies have monopolized the GMO crop industry, Jacob said, making it difficult for individual, small-scale farmers to make a living. However, while some farmers may be driven out of business, those that work with the biotech companies may reap the economical benefits of increased crop yields and reduced pesticide costs, the USDA has said.

Labeling of GMO food is important to a majority of people in the U.S., according to polls conducted by Consumer Reports, The New York Times and The Mellman Group. People strongly in favor of GMO labeling believe that consumers should be able to decide whether they wish to purchase genetically modified foods.

However, Jacob said, there is no clear scientific evidence that GMOs are dangerous for human health.

Genetically modifying animals and humans

Today, livestock are often selectively bred to improve growth rate and muscle mass and encourage disease resistance. For example, certain lines of chickens raised for meat have been bred to grow 300 percent faster today than they did in the 1960s, according to a 2010 article published in the Journal of Anatomy. Currently, no animal products on the market in the U.S., including chicken or beef, are genetically engineered, and, therefore, none are classified as GMO or GE food products.

For the past several decades, researchers have been genetically modifying lab animals to determine ways the biotechnology could one day help in treating human disease and repairing tissue damage in people, according to the National Human Genome Research Institute. One of the newest forms of this technology is called CRISPR (pronounced "crisper").

The technology is based on the ability of the bacterial immune system to use CRISPR regions and Cas9 enzymes to inactivate foreign DNA that enters a bacterial cell. The same technique makes it possible for scientists to target a specific gene or group of genes for modification, said Gretchen Edwalds-Gilbert, associate professor of biology at Scripps College in California.

Researchers are using CRISPR technology to search for cures for cancer and to find and edit single pieces of DNA that may lead to future diseases in an individual. Stem cell therapy could also make use of genetic engineering, in the regeneration of damaged tissue, such as from a stroke or heart attack, Edwalds-Gilbert said.

In a highly controversial study, at least one researcher claims to have tested the CRISPR technology on human embryos with the goal of eliminating the potential for certain diseases. That scientist has faced harsh scrutiny and was placed under house arrest in their home country of China for some time.

The moral dilemma

The technology may be available, but should scientists pursue genetic modification studies in humans? It depends, said Rivka Weinberg, a professor of philosophy at Scripps College.

"When it comes to something like a [new] technology, you have to think about the intention and different uses of it," Weinberg said.

The majority of medical trials for treatments that make use of genetic engineering are performed on consenting patients. However, genetic engineering on a fetus is another story.

"Experimentation on human subjects without their consent is inherently problematic," Weinberg said. "There are not only risks, [but also] the risks are not mapped out. We don't even know what we are risking."

If the next-generation technology were available and shown to be safe, the objections to testing it in humans would be minimal, Weinberg said. But that's not the case.

"The big problem with all of these experimental technologies is that they are experimental," Weinberg said. "One of the main reasons why people were so horrified by the Chinese scientist who used CRISPR technology on embryos is because it is such an early stage of experimentation. It is not genetic engineering. You are just experimenting on them."

The vast majority of the proponents for genetic engineering realize that the technology isn't ready to be tested on humans yet, and state that the process will be used for good. The goal of genetic modification, Jacob said, "has always been to tackle problems currently facing human society."

Further reading:

Rachel Ross
Live Science Contributor

Rachel Ross is a science writer and editor focusing on astronomy, Earth science, physical science and math. She holds a Bachelor of Arts in Philosophy from the University of California Davis and a Master's degree in astronomy from James Cook University. She also has a certificate in science writing from Stanford University. Prior to becoming a science writer, Rachel worked at the Las Cumbres Observatory in California, where she specialized in education and outreach, supplemented with science research and telescope operations. While studying for her undergraduate degree, Rachel also taught an introduction to astronomy lab and worked with a research astronomer.