The DNA content of an individual cell can be measured by applying a DNA-specific dye to the cell and then passing it through an instrument that measures the staining intensity. A new drug was tested on a population of rapidly dividing tumor cells, and the DNA contents of the treated cells were analyzed and compared with those of untreated cells. Dye Intensity % untreated cells % treated cells
<10 0 20
10 10 5
20 55 60
30 5 5
40 30 10
Explain the data for the untreated cells. Which cells are in G1? What do the data indicate about how much time cells spend in G1 relative to other phases?