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BIOLOGICAL INQUIRY: A Workbook of Investigative Cases
3. Interpret the graph in Figure 10.2 by answering the following questions.
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% Increase in Number of Tumors/Mouse
300
250
200
150
100 34
36
38
40
42 44 46 Weeks on Test
Water
48
50
52
Cyclopamine
Figure 10.2 Effect of cyclopamine on BCC tumor formation in UVB-irradiated mice. (After Athar et al., 2004) (Note: The asterisk means the differences between the two treatments are statistically significant.)
a. On the basis of the shape of the curves, explain the patterns of tumor production in control and experimental mice in weeks 34–52. For control mice, a sigmoid-shaped curve is shown, in which cancer production is slow between weeks 34–39. Between weeks 39 and 41, there was rapid production of tumors with a slowing of rate between weeks 42 and 46. There was no further increase in tumors until week 52. For mice given cyclopamine, there is little or no increase in tumors from weeks 34 to 39. A slow but steady increase in rate of tumor production is seen between weeks 40 and 46. Little subsequent increase in tumors is seen after week 47. This is also a sigmoid curve but much flatter.
b. What is the overall percentage increase in tumors for control versus experimental mice? Overall, a 300% increase in tumor production for water-treated control mice. Overall, approximately a 200% increase in number of tumors per treated mouse.