When a population of cells is examined with a microscope, thepercentage of the cells in the M phase is called the mitotic index. The greater the proportion ofcells that are dividing, the higher the mitotic index. In a particular study, cells from a cell cultureare spread on a slide, preserved and stained, and then inspected in the microscope. A hundred cellsare examined: 9 cells are in prophase; 5 cells are in metaphase; 2 cells are in anaphase; 4cells are in telophase; the remainder, 80 cells, are in interphase. Answer the followingquestions:

a. What is the mitotic index for this cell culture?

b. The average duration for the cell cycle in this culture is knownto be 20 hours. What is the duration of interphase? Of metaphase?

c. Going back to the living culture of these cells, the averagequantity of DNA per cell is measured. Of the cells in interphase, 50% contain 10 ng (1nanogram = 10-9 g) of DNA per cell; 20% contain 20 ng DNA per cell; theremaining 30% of the interphase cells have amounts of DNA between 10 and 20 ng.Based on these data, determine the duration of the G1, S, and G2 portions ofthe cell cycle.