Genetically engineered maize. Conceptual computer illustration of a strand of DNA with a genetically modified (GM) corn cob. A DNA autoradiogram is seen at lower left. DNA (deoxyribonucleic acid) is the molecule which controls the growth and development of all living things. It is made of strands linked by pairs of bases (spheres). The black bands on the autoradiogram represent the positions of the bases on the DNA molecule. Corn, or maize (Zea mays), is a crop grown in the warmer parts of the world. Genetic engineering involves altering an organism's DNA to impart beneficial traits. In crops, these often increase resistance to disease or protect the plants from weedkillers.