Genetically-modified maize. Cob of genetically- modified (GM) maize (Zea mays). Maize, commonly known as corn, is grown for food in tropical and subtropical regions worldwide. Genetic modification of plants involves altering their DNA (Deoxyribonucleic acid), the chemical which controls every part of an organism's growth and development. This modification may give the plant desirable characteristics, such as resistance to disease and herbicides. In this case the maize has been modified to improve its resistance to the glyphosinate type weed killer. It is controversial whether GM foods are safe to eat.