Passage I

The mitotic index (MI) for a group of cells is calculated as follows:

MI =

Figure 1 shows the average MI for onion root tip cells as a function of their distance from the root cap.

Five hundred mitotic onion root tip cells were examined. Figure 2 shows the number of cells in each of the 4 mitotic phases.

Figure 3 shows 4 onion root tip cells (Cells 1-4), each of. which is in 1 of the 4 mitotic phases. In Figure 3, each phase is shown once. However, the cells are not arranged in order of the phases of mitosis.

Figure 3 adapted from Peter H. Raven, Ray F. Evert, and Susan E. Eichhorn, Biology of Plants, 4th ed. @1986 by Worth Publishers, Inc.