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Interpreting Evolutionary Trees

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Unit 5 - Evolution
Biology
Title: Interpreting Evolutionary Trees
Time: 85 minutes
Established State Goals
Expectation and Indicator:
3.4.1 The student will explain how new traits may result from new combinations of existing
genes or from mutations of genes in reproductive cells within a population.
Assessment Limits:
 Natural selection (definition; effects of environmental pressure)
 Adaptations (effects on survival)
 Variation (effects on survival and reproductive success)
3.4.2 The student will estimate degrees of relatedness among organisms or species.
Assessment Limits:
 Classification (recognize relationships among organisms; distinguish between prokaryotes and
eukaryotes)
 Anatomical similarities (evolutionary relationships; homologous structures)
 Similarities of DNA base and/or amino acid sequence (including results from gel
electrophoresis)
Harford County Goals
Objectives:
 Analyze and explain the relationships
illustrated in an evolutionary tree.
Guiding Questions:
How are evolutionary relationships
illustrated? What do evolutionary trees
say about the relationships among the
species in the trees?
Background and Teacher Notes
Connections in Context (previous and future related topics):
This lesson should follow lessons in this unit that how new species evolve, how evidence can be
used to identify evolutionary relationships, and how evolutionary relationships can be illustrated
on evolutionary trees.
This lesson should precede the lesson in this unit on classification so students understand that
organisms are classified based on evolutionary relationships and how those relationships are
illustrated.
EV-149
Unit 5 - Evolution
Biology
Major Concepts and Science Skills:
Students should understand:
 that the Earth is old and that life has been evolving for an extremely long period of time.
 that fossils illustrate life’s history and evolutionary relationships.
 how variation, along with other observations that Charles Darwin made, cause
populations to evolve by natural selection.
 how different environmental changes will affect traits in a population.
 how reproductive isolation leads to the evolution of new species.
 how evidence, including fossil, anatomical, embryological, and biochemical, are used to
identify evolutionary relationships.
 how to illustrate and interpret evolutionary relationships on evolutionary trees.
Materials:
Prentice Hall Supporting Materials:
Copies of student activity
Chapter 18: 447-463
Vocabulary:
Essential:
Adaptive radiation/
divergent evolution
Common ancestry
Degrees of relatedness
Evolution
Evolutionary tree/cladogram
Population
Species
Important:
Punctuated equilibrium
Good to Know:
Teacher Tips:
A detailed evolutionary tree illustrating the relationships of 3,000 species based on rRNA
sequences can be downloaded at
http://www.zo.utexas.edu/faculty/antisense/DownloadfilesToL.html It is recommended that if
this evolutionary tree is printed, that it be printed at least 54 inches X 54 inches so it can be
easily read. Credit for the tree is to be given to David M. Hillis, Derrick Zwickl, and Robin
Gutell, University of Texas.
Students should already understand how to build evolutionary trees from evidence. This exercise
will extend their ability to explain what is depicted. Many students will often read an
evolutionary tree incorrectly from left to right, instead of correctly from top to bottom. The
branching pattern of the tree needs to be emphasized, where each branch point (node) represents
a common ancestor of the species at the tips of the branches. Be careful to explain that one
species in the tree did not evolve into another, but that the species in the tree share a common
ancestor that was not any particular species illustrated in the tree.
The multiple choice questions with their answers and an extension activity can be accessed
online for free at http://www.sciencemag.org/cgi/content/full/sci;310/5750/979/DC1
The use of evolutionary trees to illustrate the evolutionary “story” of a species can be helpful in
allowing students to visualize the evolutionary process and the relationships among species.
Evolutionary trees also help students to understand that evolution happens not in a predetermined
“chain”, but as a blind, branching “tree”.
EV-150
Unit 5 - Evolution
Biology
A discussion of punctuated equilibrium theory would be appropriate at this time as an extension
to clarify the misconception that evolution is continually working at a constant rate.
Evolutionary trees usually have smooth, straight branches, which do not show the actual
punctuated evolutionary history of species.
Special Education:
Accelerated Education:
 Place students into lab groups or pairs that
balance the readiness levels of each
student. Students who excel can model
behavior and assist with task comprehension
and completion.
 Provide a copy of notes with the extra
information deleted and only necessary
information presented.
 Provide worksheets that are clear, concise and
free from clutter.
 Provide worksheets for graphs/charts, or assist
with setting up graphs/charts.
 Periodically check for understanding by having
the student repeat back what they are being
asked to do.
 May need to reduce the number of Tree multiple
choice questions.
Inquiry Approach:
Citation:
Baum, D, Smith, S, & Donovan, S (2005). The tree-thinking challenge. Science. pp. 310, 979-980.
EV-151
Unit 5 - Evolution
Biology
Evolutionary tree illustrating the relationships of 3,000 species based on rRNA sequences
A pdf file can be downloaded for free at:
http://www.zo.utexas.edu/faculty/antisense/DownloadfilesToL.html
It is recommended that if this evolutionary tree is printed, that it be printed at least 54 inches X
54 inches so it can be easily read. Credit for the tree is to be given to David M. Hillis, Derrick
Zwickl, and Robin Gutell, University of Texas.
Interpreting Evolutionary Trees
EV-152
Unit 5 - Evolution
Biology
Student Activity
Procedure:
1. Look at the image of the two evolutionary trees and answer the question that follows.
2. Complete the ten multiple choice questions and share the answers with the class.
Conclusions:
Examine the illustration below of two evolutionary trees.
Tree #1
Tree #2
1.
How many common ancestors are depicted in each tree?
2.
Which direction is time moving through the trees?
3.
Which evolutionary tree accurately illustrates the evolutionary relationships among the
five species? Explain.
EV-153
Unit 5 - Evolution
Biology
Answer the questions below.
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Unit 5 - Evolution
Biology
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Unit 5 - Evolution
Biology
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Unit 5 - Evolution
Biology
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Unit 5 - Evolution
Biology
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Unit 5 - Evolution
Biology
Teacher Answers
Examine the illustration below of two evolutionary trees.
Tree #1
Tree #2
1.
How many common ancestors are depicted in each tree? 4
2.
Which direction is time moving through the trees? up
3.
Which evolutionary tree accurately illustrates the evolutionary relationships among the
five species? Explain.
Both illustrate exactly the same evolutionary relationships. Their branches are simply
rotated at common ancestors (nodes). Rotating the branches left or right does not change
the evolutionary relationships in the tree.
EV-159
Unit 5 - Evolution
Biology
EV-160
Unit 5 - Evolution
Biology
EV-161
Unit 5 - Evolution
Biology
EV-162
Unit 5 - Evolution
Biology
EV-163
Unit 5 - Evolution
Biology
EV-164
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