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ABOUT one in 20 flowering plants are naturally transgenic, carrying bacterial DNA within their genomes. The added genes can make them produce unusual chemicals, and the species they have been found in include tea, bananas and peanuts.

Other plants that carry bacterial genes include sweet potatoes, yams, American cranberries, Surinam cherries and the hops used to flavour beer. What effect the added genes have on the plants that contain them is still far from clear. “We are only at the start of this,” says Léon Otten at the Institute of Molecular Biology of Plants in Strasbourg, France. …