Detection of genetically modified organisms
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The detection of genetically modified organisms in food or feed is possible by biochemical means. It can either be qualitative, showing which genetically modified organism (GMO) is present, or quantitative, measuring in which amount a certain GMO is present. Being able to detect a GMO is an important part of GMO labeling, as without detection methods the traceability of GMOs would rely solely on documentation.
Polymerase chain reaction (PCR)
The polymerase chain reaction (PCR) is a biochemistry and molecular biology technique for isolating and exponentially amplifying a fragment of DNA, via enzymatic replication, without using a living organism. It enables the detection of specific strands of DNA by making millions of copies of a target genetic sequence. The target sequence is essentially photocopied at an exponential rate, and simple visualisation techniques can make the millions of copies easy to see.
The method works by pairing the targeted genetic sequence with custom designed complementary bits of DNA called primers. In the presence of the target sequence, the primers match with it and trigger a chain reaction. DNA replication enzymes use the primers as docking points and start doubling the target sequences. The process is repeated over and over again by sequential heating and cooling until doubling and redoubling has multiplied the target sequence several million-fold. The millions of identical fragments are then purified in a slab of gel, dyed, and can be seen with UV light. It is not prone to contamination. Irrespective of the variety of methods used for DNA analysis, only PCR in its different formats has been widely applied in GMO detection/analysis and generally accepted for regulatory compliance purposes. Detection methods based on DNA rely on the complementarity of two strands of DNA double helix that hybridize in a sequence-specific manner. The DNA of GMO consists of several elements that govern its functioning. The elements are promoter sequence, structural gene and stop sequence for the gene.[1]
Quantitative detection
Quantitative PCR (Q-PCR) is used to measure the quantity of a PCR product (preferably real-time, QRT-PCR).[2] It is the method of choice to quantitatively measure amounts of transgene DNA in a food or feed sample. Q-PCR is commonly used to determine whether a DNA sequence is present in a sample and the number of its copies in the sample. The method with currently the highest level of accuracy is quantitative real-time PCR. QRT-PCR methods use fluorescent dyes, such as Sybr Green, or fluorophore-containing DNA probes, such as TaqMan, to measure the amount of amplified product in real time. If the targeted genetic sequence is unique to a certain GMO, a positive PCR test proves that the GMO is present in the sample.
Qualitative detection
Whether or not a GMO is present in a sample can be tested by Q-PCR, but also by
Event-specific vs. construct-specific detection
When producers, importers or authorities test a sample for the unintended presence of GMOs, they usually do not know which GMO to expect. While EU authorities prefer an event-specific approach to this problem, US authorities rely on construct-specific test schemes.
Event-specific detection
An event-specific detection searches for the presence of a DNA sequence unique to a certain GMO, usually the junction between the transgene and the organism's original DNA. This approach is ideal to precisely identify a GMO, yet highly similar GMOs will pass completely unnoticed. Event-specific detection is PCR-based.
Construct-specific detection
The construct-specific detection methods can either be DNA or
Shortcomings of current detection methods
Currently, it is highly unlikely that the presence of unexpected or even unknown GMOs will be detected, since either the DNA sequence of the transgene or its product, the protein, must be known for detection. In addition, even testing for known GMOs is time-consuming and costly, as current reliable detection methods can test for only one GMO at a time. Therefore, research programmes such as Co-Extra are developing improved and alternative testing methods, for example DNA microarrays.
Alternative detection methods
Improving PCR based detection
Improving PCR based detection of GMOs is a further goal of the European research programme Co-Extra. Research is now underway to develop multiplex PCR methods that can simultaneously detect many different transgenic lines. Another major challenge is the increasing prevalence of transgenic crops with
Detecting unknown GMOs
Almost all transgenic plants contain a few common building blocks that make unknown GMOs easier to find. Even though detecting a novel gene in a GMO can be like finding a needle in a haystack, the fact that the needles are usually similar makes it much easier. To trigger gene expression, scientists couple the gene they want to add with what is known as a
Near infrared fluorescence (NIR)
Near infrared
Controls by country
European Union
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Switzerland
The Cantons of Switzerland perform tests to assess the presence of genetically modified organisms in foodstuffs. In 2008, 3% of the tested samples contained detectable amounts of GMOs.[3] In 2012, 12% of the samples analysed contained detectable amounts of GMOs (including 2.4% of GMOs forbidden in Switzerland).[3] Except one, all the samples tested contained less than 0.9% of GMOs; which is the threshold that impose labelling indicating the presence of GMOs.[3]
See also
References
- ^ Schreiber, G.A. "Challenges for methods to detect genetically modified DNA in foods" (PDF). Food Control. pp. 351–352. Retrieved 13 December 2013.
- ISBN 978-1-904455-39-4.
- ^ a b c (in French) Fabien Fivaz, "OGM en augmentation dans nos assiettes malgré le moratoire", Stop OGM infos, no. 53, November 2013.
External links
- Co-Extra: Research on co-existence and traceability investigates new and improved detection methods
- European Network of GMO Laboratories Archived 2007-07-01 at the Wayback Machine develops and standardises detection methods
- Institute for Reference Materials and Measurements provides reference material for GMO detection
- GMO Detection Methods Database the Institute for Health and Consumer Protection (IHCP) provides validated GMO Detection Methods