Genetically Modified Crops and Gene Flow

April 2007
Written by Jennifer Hood

Tags: agriculture, environment, GM, evolution

What are genetically modified crops?
Farmers all over the world have been modifying plants grown as crops for thousands of years. Starting with wild edible plants, people grew the seeds from only the best performing plants, and bred the best plants together to get the traits they liked, eventually creating the crops we use today.

Genetically modified (GM) crops are a new and more powerful way to modify crop plants at the molecular level.

By inserting new genes that come from other plants and unrelated organisms, like bacteria, fish, insects or other animals, scientists can create a new plant that could have never been produced through traditional plant breeding. GM crops can be created to be resistant to chemical weed killers, such as Monsanto’s “round-up ready” soybean, which can resist the weed killer called “round-up”. Crops have also been made to better resist diseases and pests, like Bt-corn, which was modified to produce a toxin normally made by a bacterium that kills insect pests. GM crops have even been developed to contain vaccines to human viruses, like tomatoes that contain a Hepatitis B vaccine!

What happens when these GM crops are planted in the fields?
The adoption of GM crops around the world has led scientists and others to wonder if these crops are dangerous to natural and agricultural ecosystems. “Environmental risks” are unknown or uncertain consequences that might be caused by the use of GM crops. These risks include changes to wild plants growing near a GM farm field, changes in the kinds of insects, birds and mammals that eat these wild plants (biodiversity), evolution of new and stronger diseases that affect wild plants and crops, and changes to crops in other farmer’s fields. The main cause of these potential problems is gene flow—the fact that GM crops are not isolated from the environment around the farm field, and the new genes present in GM crops might be able to “escape” to the wild.

How can genes escape, or, what is gene flow?
Genes can escape through gene flow – meaning they can move from a crop plant to a wild plant or another crop in a similar way to how genes move from parents to children. Plant genes from the male plant are carried in the pollen to the female part of the flower where the egg (which also contains plant genes) is fertilized. Food crops that were created over thousands of years are still very similar to their cousins in the wild, and they can interbreed, or “hybridize”.

Scientists are aware of many cases where the pollen from a crop, carrying crop genes fertilized an egg of a wild relative, resulting in offspring that have genes from both crop and wild plant. These new plants are called hybrids. If the original crop was a GM plant, then the hybrid may end up with the modified genes from the GM crop, and it could spread those genes through the wild plant population when it reproduces.

How might new genes harm wild plants and the environment?
If the new genes incorporated into a wild plant give the plant no special advantage or help it to survive, it is unlikely to really make much of a difference in the plant population. But if the new genes give the plant some advantage over other members of its species then that plant may be able to survive longer and have more offspring, making the new genes more common. It’s a classic example of the evolutionary principle of “survival of the fittest.”

So the impact of the gene on wild plants has a lot to do with the kind of gene that manages to escape, and the type of plant into which it ends up.

Because the genes that are put into GM crops are designed to give crops a special advantage, it is quite likely that many of these genes would also give wild plants an edge.

Take the example of disease resistance. Scientists have discovered genes they can insert into crop plants that give them extra resistance to diseases. While this may be really good news for the farmer who is able to have healthy crops that resist disease, it may be bad news for the natural environment, and even the farmer if the gene escapes by gene flow. If a GM-hybrid wild plant becomes stronger because of its new resistance gene, it may turn into a weedy pest and take over, forcing other plant species and the animals that rely on them for food to go locally extinct. The new hybrid plant might also turn into a weed problem for the farmer, and will have to be controlled with a chemical weed-killer.

Another problem with having disease resistant genes in crops and wild plants is that the diseases themselves might be affected. Diseases can evolve a way to cope with crop’s resistance genes, which can make the GM crop’s resistance genes not very effective over time- and this can mean unexpected damage to crop plants, and the wild plant populations that have come to rely on their new GM resistance gene.

So what can we do?
Scientists realize GM crops may pose a risk to the environment and are working on ways to contain genes that might escape to wild plants. One way of doing this is to insert the new gene into the chloroplast of the cell instead of the nucleus. This works because pollen only carries genes from the nucleus and does not carry a chloroplast or chloroplast genes. GM crop pollen may be able to fertilize wild plants, but the new gene does not go with it. However, if wild pollen fertilizes a crop plant (containing the chloroplast), then the hybrid will still contain the gene.

Right now it is difficult to say with certainty what the effects of GM crop technology will be. While researchers are trying to better understand the effects and come up of with ways to deal with them, society needs to understand the risk of the uncertainty in the use of GM crops.