Genetically Modified (Transgenic) Organisms

Learning Objectives

  1. Define Genetically Modified Organisms (GMOs) as transgenic organisms, explain how scientists used genetic engineering techniques to produce them, and give some examples.
  2. Explain why the transgenes in genetically modified food are safe for human consumption.
  3. Apply your knowledge of plant reproduction to explain how GMOs could hypothetically release transgenes into wild populations, and give some examples of the known risks for transgene spread.
  4. List different applications and uses for genetic modification that directly benefit or harm humans, other species, and/or the environment.

 

Transgenic organisms contain one or more genes from another organism (not inherited)

Genetically modified organisms (GMOs) are more accurately called transgenic organisms where trans means on or from “the other.” A transgene is a gene that comes from outside the genome. Bacteria acquire transgenes naturally all the time through horizontal gene transfer. However, the precise use of transgene refers to a gene inserted into a genome by artificial means. Scientists can do this very precisely now, which is how we make insulin for diabetics, how we prevent crop species susceptibility to insects or fungi or even from dying from herbicides. 

We learned in class last time how scientists use transformation to genetically engineer the desired genome, then cloning up millions of copies using molecular cloning in bacteria. That lab technique can work when the desired outcome is to make lots of a specific protein, like insulin, in a controlled lab setting. So, how do we apply this idea to crops that have to survive and thrive in the natural environment, like out in a cotton field? Transgenes can allow a cotton plant to express genes for a toxin that prevents the pink bollworm insect from surviving, but that gene wouldn’t be much use in a lab where boll worms never venture. Instead, the gene needs to be transferred into the plant itself so it can work in the environment where the insects are.

The most common technique to move the transgene, or gene of interest, into a multicellular organism is to make use of a plant pathogen called Agrobacterium, a bacterium that can invade a damaged plant through the soil (Showalter et al 2009 J Insect Sci. 9:22). Insert a plasmid with the gene of interest into Agrobacterium, let the Agrobacterium infect a plant, and then the gene of interest can integrate into the infected plant cell’s genome. Researchers screen plants for the presence of the gene of interest, then breed plants with the gene to increase the frequency of the transgene and make it homozygous.

Watch Hank Green’s explanation of why transgenic organisms are not bad:

 

Transgenes in genetically modified food are safe for human consumption

So, you’ve bought a new pair of jeans and you love them. You wear them every single day…you even sleep in them. They were made with transgenic cotton, so your skin, the largest organ in your body, is in constant contact with the transgenic fibers of the cotton. Should you be worried that you’ll absorb the bollworm toxin from the cotton through your skin and be poisoned by it? The answer is no, and here’s why:

  1. The cotton is dead plant tissue. Its cells are no longer expressing genes, including that toxic transgene.
  2. The transgene was toxic to bollworm larvae, not to mammals.

Okay, so the transgenic cotton you wear cannot harm you. But what about the transgenic food we eat, like tomatoes, soy, or corn? Most of the corn and soy grown in the US is transgenic. Why shouldn’t we worry about eating transgenic (versus non-transgenic) plants?

  1. As with cotton, the food plant DNA and the transgenes in it are in the plant cells, which are dead by the time they reach your table, much less enter your digestive system. They do not have the ability to express themselves, and the proteins those genes make are not harmful to mammals.
  2. Your body absorbs nutrients (vitamins, minerals) and sugars from food in the intestine. The plant matter itself, including the DNA, stays on the “outside” of your body, because the digestive system is basically just a long tube that runs through your body but never connects to the inside. It only has two openings, the mouth and anus, and both of those go to the outside of the body.

How do transgenes affect the environment?

Transgenes in fertile crop species could hybridize into nearby weedy relatives of those crop plants. For instance, corn can hybridize with wild teosinte, crop rapeseed (grown for canola oil) can mate with wild rapeseed plants, etc. So GMOs can hypothetically release transgenes into wild populations. Hybridization of a transgene for insecticide toxin or of herbicide resistance could destroy an insect population or make un-killable weeds. While researchers have evidence that some transgenes have escaped into the wild, notably for rapeseed, which is a crop that is still cultivated where its natural relatives live nearby. The immediate result does not seem to be super weeds or loss of insect populations. However, we may not have enough data yet to know what the long term implications are.

Another type of environmental impact occurs when the transgenic crop is engineered to survive herbicides like Monsanto’s Roundup. Plant crops that are transgenically resistant to herbicides, can be treated with herbicides to kill the weeds that compete with them for nutrients and water. The excess herbicide then sits in the soil, and runs off into the surrounding environment. What’s the half-life of the herbicidal chemicals? What other species do they harm besides the targeted weeds?

Finally, please download and read through this science-based look at Genetically Engineered Crops: experiences and perspectives, published in 2016 by the National Academies of Sciences, Engineering and Medicine. (The National Academies comprises experts in those fields and includes in its roster over 300 Nobel prize winners.)

In class, we’ll discuss the ideas above and add bioremediation by transgenic organisms into the mix.