Plant genes are normally switched on and off in particular plant tissues according to the plant s needs and environmental conditions. However, inserted genes in a GM plant are always switched on in every plant cell. In the United States, GM insect resistant crops are starting to become less effective, as the insect pests they were designed to resist rapidly develop tolerance. Existing genes may be disrupted or switched on by the inserted promoter, leading to unexpected effects. Genes cannot be considered in isolation.
Genes tend to work in groups in an organised but barely understood way.
Introducing new genes and DNA sequences, in combinations never ever known before, will disrupt gene function in ways we simply cannot predict. In the short term, growing GM crops is likely to cause a switch to glyphosate and glufosinate ammonium from other herbicides. However Glufosinate ammonium causes birth defects in experimental animals, causing premature cell death in the immature brain by a process called apoptosis. Maize is frequently grown year after year on the same site without crop rotation, yet in the crop trials maize is only for one year, so any longer term effects of using glufosinate ammonium won t be measured. And of course, the levels of other pesticides used on these crops will not decrease either.