The genetic modifications of corn has focused primarily on insect resistance and improvements in growth rate and yield. Few efforts have been made to increase the nutritional quality of important food crops. Golden rice is a notable exception to this. Unfortunately, politics have made it difficult to get this product out to under-nourished farming communities. Genetic engineering is not merely selective breeding on a faster time scale.
Genetic engineering involves actually inserting DNA from other species into the DNA of a crop plant.
This type of genetic change cannot happen using selective breeding or hybridization.