Square tomato. Conceptual image of a tomato that has a cuboid shape. This could represent a tomato that has been genetically modified to form this shape to allow more efficient packaging and easier slicing. Genetically modified (GM) tomatoes are commercially available, but are still round. Such changes in shape can also be achieved by growing the fruit in a suitably shaped container. Genetic modification is the alteration of an organisms DNA (deoxyribonucleic acid) to create inherited changes. For food crops, the changes can include improved shelf-life and resistance to disease.