This question is easier than it seems! It can be hard to understand exactly what a GMO is, in everyday language. You have come to the right place to understand.
Most GMO crops have been modified using DNA from a foreign species. Scientists have isolated a desired genetic trait from one species, usually a bacteria or a virus, and introduced it into the cells of the target plant or animal. Because the receiving plant does not recognize this DNA, other DNA from a source the plant would recognize is included as a vehicle; like the cauliflower mosaic virus.
Scientists cannot know if the transfer was successful right away, so they include an antibiotic resistant marker gene before transfer. The cells are then washed in antibiotics, and whatever survives the process is considered a success, and the cells are duplicated to become the seed for our crops.
One of the most common GMO crops are Roundup Ready. These crops have had DNA from a bacteria added which makes it so the food crop will not die when sprayed with Roundup or glyphosate. This allows farmers to spray the entire field with Roundup.
Another common type of GMO are crops that express the BT toxin. Bacterial thuringiensis is a soil dwelling bacteria used to create a toxin used in organic farming. However, with traditional use, the toxin could be washed off. Now, scientists have added DNA from BT to the cells of our crops. As a result the crop itself becomes a pesticide by expressing the bt toxin. If a pest eats the plant, the pest dies. When the crops are modified in this way, they are registered with the EPA as a pesticide. They are in our food supply and they are unlabeled.
GMOs are sometimes confused with selective breeding or hybridization. In fact proponents of this technology will often say scientists have simply found a way to speed up breeding techniques which have been used for thousands of years.. This is NOT true! Selective breeding and hybridization have been around for thousands of years. Genetic modification is new and has only been in our food supply since 1996.
It is important to understand the difference between selective breeding, hybridization and GMOs. With traditional breeding you could take two corn varieties and create a new corn. You could take two apple varieties and create a new apply. With GMO you can combine to completely foreign species, which would never combine in nature.
In the past, fish genes have been added to tomatoes to help them resist frost. They were sold in the US but have been removed from the market. Genetically modified salmon is in the process of being approved. There are additional GMO products in the pipeline for approval.
While these next examples are not in our food supply, it is important to know what this science is capable of. It is also important to know that the current policy regarding labeling and human safety testing is lax enough that some of these could be introduced to our food supply without testing or labels.
- Jellyfish genes have been added to pigs and kittens resulting in organs and other body partswhich glow green.
- Spider DNA has been added to goats to create goats whose milk contains spider web silk.
- Cows in China have been modified so they produce human milk.
- There are test fields of rice which contain human blood proteins.
- The first genetically engineered babies have been born. They have DNA from 3 separate adults.
This technology is far different than hybridization and selective breeding, and should never be confused. This is a completely unnatural technology which requires no human safety testing or mandatory labeling in the US. We should not allow this industry to deliberately confuse genetic modification and traditional plant and animal breeding programs.