Becker's World of the Cell 9th Edition by Lewis Kleinsmith, Jeff Hardin, Gregory Paul Bertoni

Exercise 2

The Mitotic Index and the Cell Cycle. The mitotic index is a measure of the mitotic activity of a population of cells. It is calculated as 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. Autoradiographic analysis indicates that the G2 phase lasted 4 hours.
(a)What is the mitotic index for this population of cells
(b)Specify the proportion of the cell cycle spent in each of the following phases: prophase, prometaphase, metaphase, anaphase, telophase, Gl, S, and G2.
(c)What is the total length of the cell cycle
(d)What is the actual amount of time (in hours)spent in each of the phases of part b
(e)To measure the G2 phase, radioactive thymidine (a DNA precursor)is added to the culture at some time f, and samples of the culture are analyzed autoradiographically for labeled nuclei at regular intervals thereafter. What specific observation would have to be made to assess the length of the G2 phase
(f)What proportion of the interphase cells would you expect to exhibit labeled nuclei in autoradiographs prepared shortly after exposure to the labeled thymidine (Assume a labeling period just long enough to allow the thymidine to get into the cells and begin to be incorporated into DNA.)