Chapter 24, Problem 24.2PS

QUANTITATIVE The Mitotic Index and the Cell Cycle. An alternative to flow cytometry is to directly examine cells under the microscope to determine the mitotic index, the percentage of cells in mitosis at any one time. Assume that upon examining a sample of 1000 cells, you find 30 cells in prophase, 20 in prometaphase, 20 in metaphase, 10 in anaphase, 20 in telophase, and 900 in interphase. Of those in interphase, 400 are found (by staining the cells with a DNA-specific stain) to have X amount of DNA, 200 to have 2X, and 300 cells to be somewhere in between. Analysis using timed applications of BrdU indicates that the G2 phase lasted 4 hours.

1. (a) What is the mitotic index for this population of cells?
2. (b) Specify the proportion of the cell cycle spent in each of the following phases: prophase, prometaphase, metaphase, anaphase, telophase, G1, S, and G2.
3. (c) What is the total length of the cell cycle?
4. (d) What is the actual amount of time (in hours) spent in each of the phases of part b?
5. (e) To measure the G2 phase, you add BrdU to the culture at some time t, and you analyze samples of the culture for the presence of labeled nuclei at regular intervals thereafter. In which sorts of cells should you look for the first appearance of BrdU to assess the length of the G2 phase?
6. (f) What proportion of the interphase cells would you expect to exhibit labeled nuclei shortly after exposure to BrdU? (Assume a labeling period just long enough to allow the BrdU to get into the cells and begin to be incorporated into DNA.)