Pre-Tidbit Instructions
• Get out your clickers
• Get out your laptops, i-pads, i-phones, or other
internet connected device
– Go to www.codecarnival.com
– Click on the first link
– Don’t click any further!!
Natural Selection
John Burke, Matt Elrod-Erickson, Sandra
Johnson, Troy Nash, Chris Peterson, Mike
Rischbieter, Dorset Trapnell
17 May 2013
Context of Unit
• Introductory Biology course for majors
• Class of 21-50 students, already divided into
working groups of 4
• Foundational knowledge from earlier units
– Mendelian genetics
– Mechanisms of heredity
Unit Learning Goals
• Students will understand…
– the definition of natural selection
– the source(s) of phenotypic variation
– how natural selection drives evolution in a
population
Unit Learning Outcomes
• Students will be able to…
– define evolutionary fitness (relative v/s absolute)
– predict the relative importance of fertility & viability
differences to overall fitness
– identify types of selective forces and how they affect
fitness
– explain relationship between random mutation and
non-random selective processes
– predict responses to changing selective pressure
– compare and contrast outcomes of differing modes
of selection (directional, disruptive, stabilizing)
Tidbit Learning Outcomes
• Students will be able to…
– define evolutionary fitness (relative v/s absolute)
– predict the relative importance of fertility & viability
differences to overall fitness
– identify types of selective forces and how they affect
fitness
– explain relationship between random mutation and
non-random selective processes
– predict responses to changing selective pressure
– compare and contrast outcomes of differing modes
of selection (directional, disruptive, stabilizing)
Tidbit Preparation
• As part of the larger unit on natural selection,
students will have been assigned a news brief
reading assignment on Galapagos Finches
Clicker Question
According to the article, the change in beak size in
Galapagos finches was driven by _____.
A.
B.
C.
D.
competition
predation
gene flow
mutualism
Clicker Question
Where did the variation come from?
A. Some finches mutated because they needed
smaller beaks.
B. Some finches had access to more seeds, so they
grew larger beaks.
C. Undirected chance mutation in beak size
gene(s).
D. Some finches hybridized with another species
of bird with different sized beaks
Imagine a population of plants
• With mutation and no selective pressure
Parent
Offspring in
the 8 other
squares.
Biomorph Simulation
• Use control/command and +/- to adjust size of box
• Use “reset” button to reset initial population
• Take 2 minutes and get used to program
– Clicking on one of the offspring will make it the parent of
the next generation
• It will move to blue center box
• 8 new offspring will be randomly generated
• Now take 1 minute to simulate the effects of
random mutations through at least 15 generations
– Randomly select offspring with out regard to their
morphology
Clicker Question
In the previous demo, you saw all manner of
shapes and sizes in the plant population over lots
of generations when no selective pressure was
applied. What does this imply about the effects of
mutations on phenotypes?
A.
B.
C.
D.
Provide a continuous source of variation
Mutations alone do not lead to directional change
Both A and B
Neither A nor B
Imagine a population of plants
• With a selective pressure – access to sunlight
• Group activity
– Come up with a hypothesis for a morphological
change that would be advantageous in the above
scenario (2 minutes)
– Run the simulation, consistently selecting for the
morphological trait of your choice (2 minutes)
– Note: Once finished, don’t hit the reset button!!
3 possible outcomes of selecting for increased branching
In the same population of plants
• The environment changes…
• Group Activity
– Propose what might happen in the environment that
might alter/reverse the previous trend (2 minutes)
– Continue the simulation, consistently selecting for
the new morphological trait of your choice (2
minutes)
Peppered Moth Group Activity
• These are two phenotypes of the same species of moth, which is
heavily preyed upon by birds. The white morph was much more
common prior to the industrial revolution. With the rise of
industry, pollution and soot started to darken tree trunks. On a
notecard, answer the following:
1) Why are there different colors of moths? (1 minute)
2) Given the changes caused by the industrial revolution, predict what
happened to the relative frequencies of these two color morphs. Explain
your answer. (2 minutes)
3) What would happen if all the predatory birds died? Explain your answer.
(3 minutes)
Acknowledgements
•
•
•
•
•
Norris Armstrong – Facilitator Extraordinaire!
Kathrin Stanger-Hall – Director Southeast RSI
Groups 2 and 3 for their helpful reviews
Don Raber, Provost – Presbyterian College
Michelle Momany, Plant Biology Department
Head – University of Georgia
• Lynn Boyd, Biology Chair – Middle Tennessee
State University