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Metrics details Abstract Our original publication 1 contained two separate conclusions derived from two methodological approaches. Second, we attempted to establish the genomic context of transgene insertion using i-PCR. Significant homology with putative misamplifications is maintained across the length of these fragments, and the CaMV sequence was not recovered.

However, this pattern is not found in our other i-PCR sequences. A revealing pattern of discontinuity is found at at least one end of five other sequences, indicating the integration junction between the transgenic DNA and the native host genome. Our critics choose not to recognize this feature in the majority of our i-PCR data. Partial homology with retrotransposon elements in maize is common in primers designed to amplify transposon-like sequences, and is not unique to our primers.

Questions concerning the distortion of expected footprints at the DNA-integration junction certainly warrant future work. The movement of transgenes into new populations and across generations is expected to result in diverse integration patterns 2 , 3 , 4 , 5 , 6 , 7.

As altered DNA species should also be an important focus of ecological research, we disagree with our critics who assume that only intact transgenes are worthy of attention in our study. We agree that PCR-based methods are sensitive and therefore open to artefacts, but strongly disagree that the presence of these artefacts is unavoidable or uncontrollable.

The consistent performance of our controls, as reported 1 , discounts beyond reasonable doubt the possibility of false positives in our results. Nevertheless, the high sensitivity of the PCR reaction has incited some critics to request a non-PCR-based method to confirm our main statement. To address these challenges, we evaluated the same samples from our original publication 1 using DNA—DNA hybridization.

The results of these experiments continue to support our primary statement. Our analysis of Oaxacan maize is unique for several reasons. First, we wished to document changes that occur within diverse populations of landraces rather than single varieties or lines , for which no markers, restriction-enzyme digestion maps or linkage analyses have been developed.

Second, we could not have predicted which or how many specific transgenic constructs or derivatives were present in the samples that we analysed. Third, our samples of ground, pooled kernels from individual maize cobs do not represent individual genomes.

All of these factors render the application of DNA-hybridization methods difficult. To minimize confusion in interpreting the multiplicity of bands that would have been created by Southern hybridization with our samples, we chose to use dot blotting for our experiments.

We extracted genomic DNA from dry maize kernels 1. Standards containing varying amounts of transgenic material were prepared by mixing flour from our positive control Bt1 and our historical negative control 1. We generated a horseradish peroxidase-labelled DNA probe from the same base-pair fragment of the pS CaMV promoter that was amplified from our previously reported 1 positive control Bt1.

Loading homogeneity was confirmed by stripping and rehybridization of the experimental membrane with the base-pair fragment from the maize-specific zein gene 1. By using standardized mixtures of transgenic and non-transgenic maize, dot-blot hybridization suggests a ratio of transgenic to non-transgenic kernels in criollo cobs of the order of , as we had previously suggested 1 and as was confirmed by Mexican government studies 1.

This DNA-hybridization study confirms our original detection of transgenic DNA integrated into the genomes of local landraces in Oaxaca. Sample numbers coincide with those in ref. Bottom row: 1, criollo sample B1; 2, criollo sample B2; 3, criollo sample B3; 4, criollo sample A1; 5, criollo sample A2; 6, criollo sample A3; 7, Peru maize negative control P1; 8, water negative control.

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Transgenic DNA introgressed into traditional maize landraces in Oaxaca, Mexico

But some of his colleagues are now questioning the integrity of the decision-making process. Ignacio Chapela was prominent among a group of vocal protesters against the deal. Subsequently, he became embroiled in controversy after publishing disputed research suggesting that transgenes flowed from modified crops into natural maize in his native Mexico. Ignacio Chapela says that he plans to contest a decision not to grant him tenure. Credit: I. One Berkeley scientist involved in the tenure review was so upset at the handling of the case that he has broken the strict confidentiality of the process to complain.

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Berkeley accused of biotech bias as ecologist is denied tenure

Metrics details Abstract Concerns have been raised about the potential effects of transgenic introductions on the genetic diversity of crop landraces and wild relatives in areas of crop origin and diversification, as this diversity is considered essential for global food security. Direct effects on non-target species 1 , 2 , and the possibility of unintentionally transferring traits of ecological relevance onto landraces and wild relatives have also been sources of concern 3 , 4. The degree of genetic connectivity between industrial crops and their progenitors in landraces and wild relatives is a principal determinant of the evolutionary history of crops and agroecosystems throughout the world 5 , 6. Recent introductions of transgenic DNA constructs into agricultural fields provide unique markers to measure such connectivity.

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