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Superbugs: Pre-Lab 2010 Name: TEACHER’S NOTES Period: ____ Purpose/Objectives: You will grow two cultures of bacteria (Bacillus thuringiensis) for several weeks in different environments. Each week you will select for bacteria that grow in the presence of an antibiotic (streptomycin). After several weeks you will test for evidence of evolution through competition. The objectives of this exercise are to: Observe evolution in real time Practice good experimental design Complete a long-term experiment Background: Evolution means __________change in species over time_________. Evolution occurs in populations because ___environmental__ conditions ____select____ (favor) individuals that are ____better____ suited to the present environment. Experiment: PROBLEM/QUESTION: How can we cause bacteria to ____evolve____ antibiotic resistance? HYPOTHESIS: If bacteria are ________grown in the presence________ of ___antibiotic___, then they will ____evolve resistance____. 1 Minority Science Programs – School of Biological Sciences – University of California, Irvine Superbugs: Pre-Lab 2010 Element Definition Example Independent/ Manipulated Variable Dependent/ Responding Variable Control Treatments Experimental Treatments Variable that you directly manipulate to test its effect on the dependent variable. What you change in the experiment. Type of environment Variable that you measure to test the effect of the independent variable. What you measure. Bacterial growth/resistance Treatment to test for unintended experimental effects. No antibiotic (Strep-) Treatment to test for effects of the independent variable. Antibiotic (Strep+) Evolution of Antibiotic-Resistance 1. In a population of bacterial cells, some cells have a mutation for antibiotic-resistance in their DNA SELECTION 2. Cells with antibiotic-resistant mutation survive REPRODUCTION 2 Minority Science Programs – School of Biological Sciences – University of California, Irvine Superbugs: Pre-Lab 2010 3. Offspring also have antibiotic-resistant DNA mutation 3 Minority Science Programs – School of Biological Sciences – University of California, Irvine