Testing For Genetically Modified Foods

Overview

Source: Laboratories of Margaret Workman and Kimberly Frye - Depaul University

Genetic modification of foods has been a controversial issue due to debated concerns over health and environmental safety. This experiment demonstrates technical understanding of how food DNA is genetically identified, allowing for educated decision making about the safety and potential dangers of using genetically modified organisms (GMOs) in food supplies.

Polymerase Chain Reaction (PCR) is used to amplify food DNA to test for the presence of genetically modified DNA in food products. Presence of specific DNA bands is detected by using gel electrophoresis to pull extracted food DNA through a 3% agarose gel, a concentration dense enough to separate the bands of DNA containing the genetically modified DNA. Several controls are used in the electrophoresis procedure to ensure DNA is successfully extracted from test foods (plant primer), and to provide known examples of both genetically modified DNA (purchased genetically modified DNA) and non-genetically modified DNA (purchased certified non-GMO food control).

Procedure

1. Extraction of DNA From Food Samples

Add 500 µL of purchased PCR mix matrix to each of the 2 screw-cap tubes using a transfer pipet or 200-1,000 µL adjustable-volume micropipette. Pipette up and down with the pipet between each aliquot to evenly mix the PCR matrix.
Label one screw-cap tube “non-GMO” and the other “test”.
Weigh out 0.5 g of certified non-GMO food and put it into the mortar.
Add 2.5 mL of distilled water and grind with pestle for

Results

After destaining, gels can be analyzed by looking at test food lanes (Table 3) to determine if the DNA bands for the 35S promoter and NOS terminator genes are present in the known locations on the gel. Placing the gel on a UV light box can help provide increased contrast (Figure 1). Alternatively, gels can be placed on white or yellow paper to provide a contrasting background to highlight DNA bands (Figure 2).

Application and Summary

Polymerase Chain Reaction (PCR) is used to amplify DNA, allowing for a wide range of DNA lab testing. One area of testing now possible with PCR is to identify GMOs by testing for presence or absence of the DNA sequences used in the genetic modification of food crops. Typically, a crop is genetically modified to confer an advantage against natural deterrents to ideal yields, e.g. pests (Figure 3), diseases, drought conditions (Figure 4), etc. Because the advantage is gained by in