1. Genetic Modification in Papaya and Fritos® Corn Chips
Lester Rosario
University of Puerto Rico, Cayey Campus
Abstract
The purpose of this experiment was to test store-bought food products for the
presence of genetically modified organisms (GMOs). The hypothesis was: Both the papaya
and the corn chips are genetically modified organisms (GMOs). In order to test the
hypothesis, first, the DNA of papaya and corn chips was extracted. Then, in 4 PCR tubes,
20 µL of Plant Molecular Mix (PMM) were added, and in other 4 tubes, 20 µL of GMO
Molecular Mix (GMM) were added. Two tubes (one with PMM and other with GMM)
contained papaya DNA and other 2 tubes (one with PMM and other with GMM) contained
corn chips DNA. Afterwards, PCR and electrophoresis with agarose gel were carried out to
the samples. According to the data obtained, the papaya and the corn chips didn’t show a
band associated with the presence of GMO DNA sequences. However, these results were
unreliable because DNA degradation occurred.
Introduction
Currently, genetically modified (GM) foods do not have to be labeled as such in the
US and foods with less than 5% genetically modified content can be labeled "GMO-free".
In Europe and Asia, genetically modified foods do require labeling if they contain >1% GM
content. Many people think that the use of GM crops has an effect. They say that there is a
possibility to create super-weeds through cross-pollination with herbicide-resistant crops, or
that super-bugs will evolve that are no longer resistant to the toxins in pest-resistant crops.
Many are concerned with potential allergic reactions to the novel proteins or antibiotic
resistance arising from the selectable markers used to develop the crops or other unforeseen
effects on public health. Proponents of genetically modified foods argue these crops are
actually better for the environment. Fewer toxic chemicals are put into the environment and
thus fewer toxic chemicals can harm the environment and human health. In addition, these
crops can preserve arable land by reducing stresses on the land, improve the nutritional
value of food in developing countries, and allow crops to be grown on previously
unfarmable land. (Bio-Rad Laboratories, Inc.). However, one of the main difficulties
which farmers will encounter when growing GM crops is no way to contain pollen
movement. In the case of oilseed rape, researchers have found that its pollen can travel up
to 4km and can escape from fields even when they are surrounded by barrier crops to
prevent this (Thompson, 2003). This can lead to contamination of other non-GMO crops
(Simpson, 2003).
The purpose of this experiment is to test store-bought food products for the presence
of genetically modified organisms (GMOs). There are two different GMO-associated DNA
sequences: the 35S promoter of the cauliflower mosaic virus (CaMV 35S) and the

2. terminator of the nopaline synthase (NOS) gene of Agrobacterium tumefaciens. One or
both of these sequences are present in most of the genetically modified crops that are
approved for distribution in North America, Asia, and Europe. The promoter serves as a
docking site for RNA polymerase and a signal for where it should start transcribing a gene.
The terminator is the signal to stop transcription. The native promoters and terminators of
unmodified genes interact with other components of a host cell to turn genes on or off
depending on cell type and situation, but scientists can engineer the constructs for GMOs so
that the foreign gene is continually transcribed and the foreign protein is produced
throughout the entire plant. On the other hand, most plants contain in their genome a third
sequence of DNA, the photosystem II chloroplast gene, and this makes it easy to ensure
whether an extraction of DNA is from a plant or not. When using PCR and gel
electrophoresis, the DNA fragments amplified from the 35S promoter and NOS terminator
are 203 and 225 base pairs (bp) respectively, and the fragments of the photosystem II gene
is 455 bp. Basing on all this theory, the hypothesis is: Both the papaya and the corn chips
are genetically modified organisms (GMOs). (Bio-Rad Laboratories, Inc.)
Methods
Extraction of DNA from food samples
First of all, using a balance, weigh 2g of papaya and 2g corn ships separately. Then,
using a mortar and adding 5 mL of water, grind for 2 minutes the 2g of papaya and 2g of
corn ships separately. Obtain 50 µL from the slurries of papaya and corn ships and add it
respectively to 2 screwcap tubes containing 500 µL of InstaGen matrix each. Then, shake
the tubes and place them in 95°C water bath for 5 minutes. Later, place the tubes in a
centrifuge in a balanced conformation, and centrifuge for 5 minutes at max speed. Finally,
the tubes are stored in a refrigerator.
Set up PCR reactions
Label 8 PCR tubes, going from number 1 to number 8. Afterwards, in the tubes 1,
3, 5, and 7, add 20 µL of Plant Molecular Mix (PMM) and in the remaining tubes add 20
µL of GMO Molecular Mix (GMM). In the tubes 1 and 2, add 20 µL of non-GMO solution
(negative control). In the next two tubes (3 and 4), add 20 µL of GMO positive control.
Then, obtain 20 µL from the supernatant of the screwcap tube containing the papaya DNA
and add it to the tubes 5 and 6. With the corn ships DNA (inside the other screwcap tube)
do the same step, but add the supernatant to the tubes 7 and 8. Finally, place the PCR tubes
in the thermal cycler.

3. Electrophoresis of PCR products
First of all, prepare an agarose gel. Then, obtain the PCR tubes from the thermal
cycler and add 10 μl of Orange G loading dye to each sample and mix well. Load 20 μL of
the molecular weight ruler into the lanes 1 and 10, and 20 μL of each sample into the gel as
follows: non-GMO with PMM in lane 2, non-GMO with GMM in lane 3, GMO positive
control with PMM in lane 4, GMO positive control with GMM in lane 5, papaya with
PMM in lane 6, papaya with GMM in lane 7, corn chips with PMM in lane 8, and corn
chips with GMM in lane 9. Run the agarose gel for 30 min at 100 V. Once it is done, take
out the gels and place on them Ethidium Bromide with buffer. Wait for 20 minutes.
Finally, remove the Ethidium Bromide and observe the gels.
Results
Figure 1: Electrophoresis results for GMO and Plant material.
Discussion
According to the data obtained, in lane 2, where there was the negative control
which was known non GMO certified seed with plant primers, a band of 455bp was not
present. This not necessarily is an error as the plant primer, although most plants carry the
gene not all plants do. In this case it is a tested control so we did expected to observe a band
for the negative plant control. This error could be DNA degradation, wrong pipetting or
DNA extraction, etc. In lane 3, where there was the non-GMO food with GMO primers, no
band in 203bp appeared as it was expected with some possible degradation. In lane 4,
where there was the GMO-positive template with plant primers, a band in 455bp was

4. observed as expected, confirming plant DNA material. In lane 5, where there was the
GMO-positive template with GMO primer, band comprising the 203bp was shown
successfully. In lane 6, where there was the papaya with plant primers, it was observed a
band of 455bp. This means that the plant DNA of papaya was successfully extracted from
the sample. In lanes 7 and 9, the samples of papaya and corn chips respectively with GMO
primers, didn’t show neither a band of 203bp nor a band of 225bp. This means that the
papaya and the corn chips aren’t GMOs. However, DNA degradation was also observed,
so this experiment should be repeated to obtain more reliable data. Finally, in lane 8, the
corn ships with plant primers showed no significant band. This means that there was again
a problem with the sample DNA extraction most probably.
References
Bio-Rad Laboratories, Inc. Biotechnology Explorer™ GMO Investigator™ Kit
Simpson, EC et al. 2003. Gene flow in genetically modified herbicide tolerant oilseed rape
(Brassica napus) in UK. Gene Flow and Agriculture: Relevance for Transgenic Crops.
2003 BCC Symposium Proceedings No. 72 pp 75-81.
Thompson, CE et al 2003. Regional patterns of gene flow and its consequence for GM
oilseed rape. Gene Flow and Agriculture: Relevance for Transgenic Crops. 2003 BCC
Symposium Proceedings No. 72 pp 95-100.