Please read this first, then do handbook, taking notes. After handbook, use your notes to do
STEM Case
Evolution STEM Case Intro Info
Introduction: Two patients infected with
Campylobacter jejuni bacteria reportedly took
4 weeks to recover from their infection instead
of the typical 3 days. Working as a CDC researcher,
you must investigate the outbreak of multidrug resistant
bacteria and determine how evolution was involved by
tracing the source and cause of the outbreak.
Learning Objectives: STEM Cases are designed to help you learn the core concepts and
practice the critical thinking skills that characterize the work scientists do (data analysis, data
Interpretation, hypothesis and reasoning, predictions and communicating findings). You are
formatively assessed as they practice each of these skills during the Case, and teachers can
examine student performance in real time. The following concepts are addressed in the Evolution
STEM Case:

Macroevolution, microevolution, artificial selection,
natural selection, traits, alleles, fitness, selective
pressures, mutations

Overview of bacteria and antibiotics,
prescription, use of antibiotics in farming

Diversity of genes and genetic resistance

Non-random nature of evolution
AP Version Only: directional, stabilizing and
disruptive selection, more detailed exploration of
gene flow, genetic drift, founder effect, bottleneck
effect
Vocabulary: Every STEM Case and Handbook contains a
glossary containing all of the vocabulary needed for the
activity. As new vocabulary is introduced, the words are
presented as orange text - clicking the orange text opens the
glossary page for that term. The glossary can also be opened
at any time throughout the case.


over
Lesson Summary: At the start of the case study you receive an
email from a local hospital. The email states that two patients were
infected with Campylobacter jejuni (CJ bacteria) after handling raw chicken. The patients were
given antibiotics and reportedly took 4 weeks to recover from their infection instead of the typical
3 days. Working as a CDC researcher, you must investigate this superbug outbreak.
 To begin the research you travel to where the chicken came from, Monita farms. You then
collect CJ bacteria samples from the farm and determine that the percentage of bacteria that
are resistant to the antibiotic is increasing over time. The you then enter the Evolution
Handbook to learn the concepts they will need to solve the case.

The Handbook is an interactive guide that addresses the key principles of
evolution listed in the Learning Objectives section above. While in the
Handbook you interact with a variety of scenarios, each addressing a
different topic in evolution. The main aim is to equip you to identify evolution
as any change to the genetic make-up of a population and the selective
Unit 7 Natural Selection (Evolution)
2019
pressures that lead to higher reproduction rates for organisms that are more fit.

Once you have completed the Handbook, you will move on to the STEM Case to
investigate the three main ways evolution occurs: gene flow, genetic drift, and natural
selection (in the AP version, more depth is provided for gene flow and genetic drift). You
perform 3 experiments, one for each possibility, and analyze and interpret data to
hypothesize what caused the superbug. They are able to revise their
hypothesis after each experiment. At the conclusion of the case, you
write a case summary to communicate their findings and practice
scientific writing skills. They will also see a page with more information on
the severity of superbugs with links for possible further exploration.
Follow Up: You can explore more about antibiotic resistant bacteria, MRSA,
superbugs and the threat they pose via these links:

https://www.cdc.gov/mrsa/
 http://time.com/5068513/superbugs-are-nearly-impossible-tofight/
 https://www.cdc.gov/drugresistance/biggest_threats.html
Scientific Background: Multi-drug resistant bacteria, so-called
“superbugs”, are a huge problem across the world. These
bacteria have evolved due to the overuse of antibiotics by
doctors, and commercial farming. Because bacteria divide so
frequently, the occurrence of mutations happens in a
comparatively short timespan. The mutations are random and
change alleles in the bacterial DNA (some knowledge of DNA,
genes and alleles will be helpful for you). Because alleles are the
“code” that determines what proteins are made, when an allele
changes then the protein made also changes.
Many antibiotics target specific proteins in bacteria in order to kill bacteria. A change in a protein
due to a mutation can result in the antibiotic no longer working, which is called “bacterial
resistance”. For example, methicillin is an antibiotic that kills bacteria by inhibiting the synthesis
of bacterial cell walls. It works by binding to an enzyme (transpeptidase) responsible for forming
links between polymer chains in the cell wall of bacteria. Methicillin was used to treat
Staphylococcus aureus infections (now superseded by vancomycin). Over time, strains of S.
aureus have evolved in which mutations in the allele for the peptidase have resulted in methicillin
no longer being able to bind to it and inhibit the enzyme. These strains are called methicillinresistant S. aureus (MRSA) and it has become incredibly difficult to treat MRSA infections.
Natural selection is the result of changes in an
environment that cause the fitness of some individuals to
be higher than others in a population. These changes are
called selective pressures as individuals with a higher
pressure will have a higher probability of surviving and
reproducing. In bacterial resistance, the selective
pressure is the antibiotic. Because antibiotics are so
widespread in our modern society and environment, more
populations of bacteria are exposed to antibiotics. Over
time, this has led to the evolution of many superbugs that
the CDC has identified as one of the major threats to
human health.
Unit 7 Natural Selection (Evolution)
2019
Handbook Notes: Please take detailed notes as you go through the Evolution Handbook. Pay
special attention and type in the correct answers to the questions. You will then use these notes
to answer the first set of questions in the STEM Case since it has you go through the Handbook
again. And, just to be nice, I’ll even give you points for completing the notes
Microevolution
[ ]
Allele Frequency
[ ]
Natural Selection
[ ]
Fitness
[ ]
Selective Pressures
[ ]
Other Factors
[ ]
Mutations
[ ]
Review
[ ]
When you have finished the Handbook, go ahead and begin the STEM Case.
Unit 7 Natural Selection (Evolution)
2019