Cladistics

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Objective

SWBAT infer evolutionary relationships using a cladogram

Big Idea

Derived characteristics in organisms may be used to determine evolutionary relationships

Hook

5 minutes

To start this lesson I display the following image.

I pose the question, "Did the X-Box one evolve from the GameCube, or do they merely share a common ancestor?" I give students a minute to think about their answer, and then to turn to an elbow partner and share their response. Finally, I ask for one volunteer to share to the class.

I then ask my "gamer" students to inform the class about which appeared first, the X-Box One or the GameCube (even my non-gamers know that the Game Cube is older than the XBox One). I tell the students that this is an important difference between what we are looking at, and what we will be learning about today, which is cladistics

Concept Introduction

10 minutes

I write cladogram on the board, distribute the cladogram guided notes and present this video that briefly explains how cladograms work.

 

I use guided notes during this presentation to promote active engagement during the video, and help students in taking accurate notes that can be used as a study guide. Guided notes provides support to students in identifying the most important information covered.

Building a Cladogram

15 minutes

Once the students understand how to use a cladogram, the next step is to explain how to build a cladogram. In order to do this, I present the following video and have students continue using their guided notes.

I created stopping points in the embedded video in order to allow students to follow along and write down their information in their guided notes. You can find the non-annotated video on Youtube by clicking on this link.

Working Together

15 minutes

I ask the students to work with an elbow partner to complete the "now with a partner" section of the guided notes. In terms of gradual release of responsibility, this would be the "you do together" section, and it provides students an opportunity to practice what they just learned while still having another person to collaborate with in searching for the best explanation (SP7).

Note to teachers: Make sure you clarify that the students are able to recognize the traits they have to work with. I invite you to read my reflection "Assumptions Can Lead You Astray".

The cladogram building during this portion is allowing students to use tables to display and analyze data (SP4; CCC Patterns Graphs, charts, and images can be used to identify patterns in data), providing practice in evaluating information to form hypothesis (SP6) and engaging in discussions with scientific peers (SP8). 

During this section of the lesson, I am circulating the room helping partnerships that might need more coaching, and listening to their conversations to make sure students are applying these new concepts correctly.

Note to teachers: Overall, I am satisfied with the student work (SW1SW2SW3). Students were able to analyze the data from the table they created, develop a cladogram (model) correctly, and use both to determine evolutionary relationships. However, there are a couple of things lacking and that I know I will need to address with these students during the next lesson and also when teaching this lesson again. I did not mention that the trait line is drawn diagonally to represent time, and almost as importantly that their examples are simplified versions. If we were to draw the same cladogram the "space" between common ancestors should vary to represent time length of time. By not mentioning this, the students focused on traits and common ancestry, but no one mentioned how recently a trait had developed. This would perhaps have given the students a better understanding of how the more recently a shared trait develops, the more closely related the organisms may be.

Closure

5 minutes

To bring this lesson to a close, I ask the students to write post-it note in response to the following questions:

  • "What was the most surprising thing you learned today?"
  • "Why was it surprising?"

This simple exercise reveals the level of understanding of the lesson and how comfortable the students are with the material that was presented. One thing worth mentioning is that many students report that they were surprised at how easy it is to create a cladogram and use it. This sense of empowerment in the students increases engagement, and can be referenced at a later lesson when/if students struggle - "Remember how you though that cladograms were difficult, and how you found out it was actually easy? Your perseverance then paid off, which shows that if you put in the time and effort you can master this too."