Cladograms - Exploring Evolutionary Relationships

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Objective

SWBAT to analyze cladograms to reconstruct the evolutionary history of taxa.

Big Idea

Students explore cladistics - organizing living things by common ancestry and evolutionary relationships to enable us to better understand life's present diversity and evolutionary history.

Enagage

15 minutes

To engage students in lesson I have students conduct a module titled What Did T. rex Taste Like? from the University of California Museum of Paleontology.

What did T. rex taste like? is an introduction to cladistics, the most commonly used method of classification today. Cladistics organizes living things by common ancestry and evolutionary relationships, enabling us to better understand life's present diversity and evolutionary history. (MS-LS4-2. Apply scientific ideas to construct an explanation for the anatomical similarities and differences among modern organisms and between modern and fossil organisms to infer evolutionary relationships.) 

Like other methods of classification, cladistics makes use of the observable features of organisms. Cladistics also allows us to examine the ways in which features change within groups, and to observe patterns of origin and diversification over time. Unlike any other method of classification, cladistics is a powerful predictive tool, allowing us to propose hypotheses about the relationships between organisms. (CCC- Patterns - patterns can be used to identify cause and effect relationships)

This module presents a simplified version of the process used to generate cladistic analyses and demonstrates its predictive power. Typically dozens or even hundreds of features are examined before a cladogram is produced. Although in this module only structural features are used, true cladistic analyses also use biochemical, genetic and even behavioral features.

Student Directions:

1.  Students are given 15 minutes to complete Folders 1, 2, and 3.

Folder 1:  Life is very diverse, yet all living things are related.  Branching diagrams show how living things are related to each other (5 minutes) (CCC Patterns - Graphs, charts, and images can be used to identify patterns in data)

Folder 2:  Lineages can be traced back in time to find a point of common ancestry. (5 min)

Folder 3:  Cladograms illustrate evolutionary relationships based upon shared inherited features. (5 min)

2.  Students are required to write down all vocabulary words (highlighted in module) and their corresponding definitions.  These vocabulary words will be revisited during lesson.

Teacher Note: I have students work in pairs to conduct module.  Depending on reading level of class you may need to model completion of Folder 1.  Teacher should walk around and check for understanding through out module.

Explore

20 minutes

In this section of lesson students explore the building and use of cladograms for the purpose of organizing living things based on evolutionary relationships.(MS-LS4-2. Apply scientific ideas to construct an explanation for the anatomical similarities and differences among modern organisms and between modern and fossil organisms to infer evolutionary relationships.) 

1.  Students visit How to Build a Cladogram which teaches students the proper steps needed to build a cladogram. (Data Table, Venn Diagram, Cladogram).

2.  Students complete page 1 and 2 of Building a Cladogram Practice which corresponds with the content of above website.

3.  In the final part of this lesson I model (SP4 - Analyzing and Interpreting Data) how to interpret the following cladogram: 

  

4.  Students answer page 3 of Building a Cladogram Practice as I model how to interpret the diagram.

Explain

10 minutes

Now students read an article titled Phylogenetic Classification from cK-12 to gain insight to why the phylogenetic tree is such a useful tool when determining evolutionary relationships. (RST.6-8.1 - Cite specific textual evidence to support analysis of science and technical texts, attending to the precise details of explanations or descriptions.)  

Students use the Writing in the Margins strategy to interact with text. I explain this strategy, and ways to support students in using it, in my reflection.

Students also use the Clarify strategy:

Clarify

Clarify complex ideas presented in the text. Readers clarify ideas through a process of analysis, synthesis and evaluation. Pausing to clarify ideas will increase your understanding of the ideas in the text.

In order to clarify information you might...

  • Define key terms.
  • Reread sections of the text.
  • Analyze or connect ideas in the text.
  • Paraphrase or summarize ideas. 

Once students have read the article they answer the following questions:

Review

  1. What is a clade?
  2. What is cladistics, and what is it used for?
  3. Explain why reptiles and birds are placed in the same clade.
  4. Dogs and wolves are more closely related to each other than either is to cats. Draw a phylogenetic tree to show these relationships.

Elaborate

10 minutes

Next, students complete pages 4 and 5 of Building a Cladogram.

1.  Students fill in the characteristics data table.

Teacher Note:  Students may need access to a computer to conduct research if they're unsure of presence of certain characteristic.

2.  Students use data table to conduct Venn Diagram and Cladogram.

3.  In collaborative groups students complete a Carousel Feedback:

I use a Carousel Feedback strategy to build students' communication skills, while expanding individual's understanding through group information sharing. Individuals rotate from cladogram to cladogram to give feedback to the members of other groups. (SL.7.1 - Engage effectively in a range of collaborative discussions (one-on-one, in groups, teacher-led) with diverse partners on grade 6 topics, texts, and issues, building on others’ ideas and expressing their own clearly.)  

  1. Students stand in front of their own cladogram.
  2. Students rotate clockwise to the next cladogram.
  3. Each student leaves feedback (affirmations or constructive) on each cladogram they visit.
  4. Once students return to their own cladogram the read feedback and ask group members any clarifying questions.

Evaluate

5 minutes

In this section of lesson students complete page 6 of Building a Cladogram Practice.  In this exercise students are required to analyze data table, create a venn diagram, and finally build a cladogram for invertebrate species.