from Arne Holst-Jensen writing in Real-Time PCR in Food Science: Current Technology and Applications:
Genetic modification (GM) alters the phenotype of the GM organism (GMO). This is achieved through application of gene technology and modification of genetic information stored in nucleic acids. The logical choice of methodology to detect and characterise GM is therefore analytical methods targeting nucleic acids. The polymerase chain reaction (PCR) methodology has been the preferred methodology of this type for two decades, and the following paper will review its applications and derivatives in relation to detection and characterisation of GM organisms (GMOs). The need for detection, identification, characterization and quantitation of GMOs depends on issues such as the legal status of the GMOs in question (authorized or not), labeling or contractual requirements, authentication, traceability and co-existence, environmental monitoring and risk assessments. The fitness for purpose of a specific analytical method is often limited to certain applications. Guidelines to establishment of analytical strategy and method selection can be very useful to those who order as well as to those who provide GMO analyses. A fundamental distinction can be made between screening and identification methods, respectively. The former may be used to group and separate putatively GMO-free samples from samples containing GMO. Both classes of methods may provide qualitative and quantitative information, but only the identification methods can provide accurate quantitation. GMO quantification is achieved almost exclusively with real-time PCR methods, but other alternatives are also available. PCR is also commonly used in combination with other techniques such as Southern blot analyses and DNA sequencing to characterize the genetic constitution of GMOs. Over the last decade extensive resources have been put into validation and critical assessment of performance characteristics and requirements for real-time PCR based GMO detection methods. GMO analyses can be particularly challenging because quantitation is required at very low concentrations, in products of highly variable nature, and where the introduced novel sequences of different GMOs belonging to the same or different species may result in misinterpretation and analytical interference. Consequently, there is a lot to learn from this field of science also for others working with real-time PCR methods. This review will provide several examples.
Further reading: Real-Time PCR in Food Science: Current Technology and Applications