Heirloom vegetables are vegetables whose seeds have been saved for generations and passed down. By contrast, seeds from hybrid plants are not true to type and so are not good for saving. This requires that the grower purchase new seeds every year. Hybrids have been bred for specific qualities but have not been genetically modified. GMO plants have been genetically engineered. This can be done by combining DNA of different plant varieties or by introducing genes from other species, such as fish.