DNA extraction. Molecular biologist at the International Maize and Wheat Improvement Centre (CIMMYT) in Mexico City extracting DNA (deoxyribonucleic acid) from maize (Zea mays). The CIMMYT is collecting DNA from every native strain of maize in Mexico as genetic insurance against the homogenisation of commercial maize varieties. As pests adapt to attack the commercial strains most widely used, pest resistance traits from the native strains can be bred into the commercial strains to protect them. Without this insurance the world could face a major food shortage in the future. Maize is the world's most important crop, and is a staple for hundreds of millions in the Americas, Africa and Europe.