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Genetically modified tomatoes. Conceptual imagery of genetic research on tomatoes. A syringe is used to extract material from the tomatoes to analyse the DNA (deoxyribonucleic acid) it contains. DNA carries the genetic code and can be altered to produce a desired trait in crops such as tomatoes. A resistance to pests and disease is introduced or larger tomatoes could be grown. The letters are symbolic of the atoms of a chemical molecule, here an organic, carbon-containing one. Carbon (C), oxygen (O), hydrogen (H) and nitrogen (N) make up an amino acid group at upper right. The genetic code is used to assemble amino acids into the proteins and enzymes that are essential for life. (KEYSTONE/SCIENCE PHOTO LIBRARY/RICHARD PRIDEAUX)