Download Teacher`s Notes - University of California, Irvine

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____.
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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
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Minority Science Programs – School of Biological Sciences – University of California, Irvine
Superbugs: Pre-Lab 2010
3. Offspring also have antibiotic-resistant DNA mutation
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Minority Science Programs – School of Biological Sciences – University of California, Irvine