Artificial directional selection in corn (Zea mays)

    Starting with a single line of corn, different strains were selected for high or low content of oil (left) or protein (right). Note that decline of oil content ceases after about 20 generations of selection, whereas the high-line has increased nearly doubled over the same period, continues to increase linearly, and has tripled after 50 generations. The difference between the two lines is nearly 14-fold after 50 generations. There seems to be lower limit of oil content compatible with viability. In another strain, protein content has doubled over 50 generations, with a four-fold difference between the low- and hig-bred lines.