So-called terminator genes, which can make seeds sterile, never made it out of the patent office in the 1990s. Seed companies do require farmers to sign agreements that prohibit replanting in order to ensure annual sales, but Kent Bradford, a plant scientist at the University of California, Davis, says large-scale commercial growers typically don't save seeds anyway. Corn is a hybrid of two lines from the same species, so its seeds won't pass on the right traits to the next generation. Cotton and soy seeds could be saved, but most farmers don't bother. "The quality deteriorates—they get weeds and so on—and it's not a profitable practice," Bradford says.