GM crops can gain useful characteristics

1. A transgenic organism contains genetic material introduced from another species by genetic engineering.
2. A gene from the bacterium Bacillus thuringiensis can be inserted into a crop plant so its cells produce the Bt protein.
3. The protein is toxic to particular insect pests that feed on the crop, so less crop tissue is damaged.
4. Reduced pest damage can increase yield and reduce the amount of broad-spectrum insecticide sprayed.
5. Other modifications can improve nutritional content, delay ripening, produce medicine or increase tolerance of drought, salt or disease.

Benefits must be weighed against risks

1. Biodiversity is the variety of different species living in an area.
2. Pollen can transfer an inserted allele to wild relatives, where the characteristic may spread beyond the crop field.
3. Heavy use of one insecticidal trait creates selection pressure that can increase resistant pest populations.
4. A toxin may affect non-target organisms, food webs or biodiversity, so effects must be monitored.
5. Seeds may be expensive or controlled by a small number of companies, which can make farmers dependent on suppliers.
6. Potential health effects are tested before approval, but uncertainty about long-term ecological effects remains part of an evaluation.