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. EV-154 Unit 5 - Evolution Biology EV-155 Unit 5 - Evolution Biology EV-156 Unit 5 - Evolution Biology EV-157 Unit 5 - Evolution Biology EV-158 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. 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