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A Single Nucleotide Polymorphism (SNP839) in the adh1 Reference Gene affects the Quantification of Genetically Modified Maize (Zea mays L.)

The validated quantitative real-time PCR assays for the genetically modified (GM) maize events NK603, GA21 and Mon 863 measure the number of copies of the GM gene in relation to those of the maize-specific adh1 reference gene; We report here that the targeted 70 basepair adh1 region exhibits a well-known single nucleotide polymorphism that negatively affects binding of the reverse primer recommended for amplification. Furthermore, we show that the Certified Reference Materials ERM-BF414 and BF415 for the detection of GA21 and NK603, respectively, were processed from maize varieties bearing different adh1-alleles and that the same allelic polymorphism is observed among several maize varieties studied. As a results of these findings, the quantification of the GM maize events mentioned is positively or negatively biased, depending on the calibrant used in the assays and on the genetic make-up of the intermixed non ¿GM variety. We, therefore, propose to revise the quantitative detection methods for NK603, GA21 and Mon 863 maize.
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