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 QuestionAccording to the article, the change in beak size in Galapagos finches was driven by _____.

A. competitionB. predationC. gene flowD. mutualism

Clicker QuestionWhere 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 inthe 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 QuestionIn 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. Provide a continuous source of variationB. Mutations alone do not lead to directional

changeC. Both A and BD. 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