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AP Biology: Unit 7: Evolution Pod 2: Phylogeny

Unit 7: Activity 7.11 - Adapted by D. Knuffke from Scientific Argumentation In Biology: 30 Classroom Activities by V. Sampson and S. Schleigh

Copyright 2013 by the National Science Teachers Association. www.nsta.org/store

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Generate an Argument:

Evolutionary Relationships in Mammals (Genetics & Evolution)

Introduction:

One of Darwin’s most revolutionary ideas was that all living things were related. According to this theory, all living things found on Earth today are related to each other because all life on Earth shares a common ancestor. This ancestor, Darwin argued, once lived on Earth sometime in the distant past, but is now extinct. All organisms, from alligators to algae are connected to one another like branches on a giant tree of life. He came to this conclusion, in part, by examining homologous structures, such as limbs (see figure 1) that have similar structure even though they may have a very different function.

Figure 1. Homologous structures in four different vertebrate limbs

To explain similarities in the underlying anatomy of different vertebrate limbs, Darwin said they must

all be descendents from the same ancestor that had a limb with the same underlying structure found in all vertebrate limbs. Darwin argued that adaptations of organisms to their environments lead to the diversification of limbs that are seen among modern vertebrates.

Modern evolutionary biology also connects the notion of homology to the biochemical domain. Species that share many genetic similarities are considered to be more closely related than two species that have many differences in their genetic material, because the random mutations that occur during DNA replication will cause differences in the DNA sequence to accumulate in each independent species over time. Therefore, the longer it has been since two species separated from a common ancestor, the more time there

Mr.

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AP Biology: Unit 7: Evolution Pod 2: Phylogeny

Unit 7: Activity 7.11 - Adapted by D. Knuffke from Scientific Argumentation In Biology: 30 Classroom Activities by V. Sampson and S. Schleigh

Copyright 2013 by the National Science Teachers Association. www.nsta.org/store

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will have been for mutations to occur in each species. Scientists can therefore use the amino acid sequence of proteins to determine the evolutionary history of a group of organisms, because protein sequences are determined by the DNA base sequence of a specific gene. As long as the appropriate protein sequences are used in the analysis, a hypothetical relationship among species can be determined.

Figure 2 - 10 show nine different types of mammals:

All of these animals share certain characteristics, such as body hair and mammary glands, which make them mammals. They also all have certain physical characteristics that make them each unique (ex. bats have wings, elk have antlers). These differences make it difficult to determine which types of mammals are most closely related.

This has made many people wonder: Which of these mammals are the most closely related?

Day 1: Slideshow construction, and posting.

Working in pairs, use the information that follows to develop a claim that best answers this question. Once your group has developed your claim, prepare a brief slideshow that you can use to share and justify your ideas. Your slideshow should include all of the following information:

● The Research Question

● Your Claim: State the claim you are trying to support

● Your Evidence: Include genuine evidence (data, analysis, & interpretation). Make sure to

include a hypothetical cladogram showing the evolutionary relationships among the mammals.

● Your Reasoning: Provide a justification of your evidence that explains why the evidence is

relevant and why it provides adequate support for the claim.

● Organize your argument in a way that enhances readability

● Use a broad range of words, including vocabulary that you have learned in class.

● Utilize proper grammar, punctuation, and error-free spelling.

Mr.

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AP Biology: Unit 7: Evolution Pod 2: Phylogeny

Unit 7: Activity 7.11 - Adapted by D. Knuffke from Scientific Argumentation In Biology: 30 Classroom Activities by V. Sampson and S. Schleigh

Copyright 2013 by the National Science Teachers Association. www.nsta.org/store

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Post your slideshow to the class blog in a post with the labels (“argument”, “evolution”, and any others that you feel are appropriate). Make it so that anyone in our school google apps can comment on your slides.

Day 2: Commenting and Response

View and comment on at least five other group’s slideshows (use the insert menu to add a comment). Remember, as you critique the work of others, you need to decide if their conclusions are valid or

acceptable based on the quality of their claim and how well they are able to support their ideas. In other words, you need to determine if their argument is convincing or not. One way to determine if their argument is convincing is to ask them some of the following questions:

● How did you analyze or interpret your data? Why did you decide to do it that way?

● How do you know that your analysis of the data is free from errors?

● Why does your evidence support your claim?

● Why did you decide to use that evidence? Why is your evidence important?

● How does your justification of the evidence fit with accepted scientific ideas?

● What are some of the other claims your group discussed before agreeing on your claim and

why did you reject them?

Working in your group, respond to all comments that were left. Incorporate any feedback into your slideshow that you feel is appropriate, and make sure to reply to all comments left on your slideshow.

Reference Information: How to create a cladogram:

A cladogram groups organisms based on the number of similarities and differences among them. In order to construct a cladogram (figure 12 - 13), it is important to identify the characteristics those the ancestral population and those of the descendants. These ancestral traits link the members of related branches to a common ancestor. On the other hand, characteristics that are found in various evolutionary branches that differ from those of the ancestors are considered derived. In many cases, a derived characteristic is a unique modification of a shared ancestral characteristic. Derived characteristics or traits distinguish the members of one evolutionary branch from the members of another branch. A cladogram is constructed based on the presence of derived traits in two or more related taxa. Ideally, a cladogram should be based on branches that are defined by a unique derived trait that emerged only once, and are shared by all subsequent descendents. In this activity, you will need to create a cladogram for the nine different species of mammals.

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AP Biology: Unit 7: Evolution Pod 2: Phylogeny

Unit 7: Activity 7.11 - Adapted by D. Knuffke from Scientific Argumentation In Biology: 30 Classroom Activities by V. Sampson and S. Schleigh

Copyright 2013 by the National Science Teachers Association. www.nsta.org/store

4

You can construct a cladogram by following these steps:

1. Identify the taxa. These taxa will be the tips of your tree and must themselves be clades. A clade is a

group of organisms that includes an ancestor and all descendants of that ancestor (see figure 12). In this

case, your taxa are the nine species of mammals.

2. Determine the characters and examine each taxon to determine the character states. In this investigation,

you have access to the first 40 amino acids in the hemoglobin alpha protein as your characters (figure

13). Your character states, therefore, will be the different types of amino acids at each point in the

sequence.

3. Determine the order of appearance of characters. In other words, figure out the order of evolution for

each character. In this investigation, you will need to determine which mutation appeared first, second,

and so on in the alpha globin sequence.

4. Group taxa together by derived or “changed” character states. Do not group the taxa together by the

original character state.

5. Build your tree. To build it correctly, you must follow three rules:

a. All taxa must go on the endpoints of the tree, never at the nodes.

b. All notes must have a shared derived character, which is common to all taxa above the node.

c. All shared derived characters can appear only once on a tree.

Two fundamental principles are used to evaluate a cladogram: parsimony and robusticity. Parsimony is a

principle that states that when there is more than one way to draw a cladogram and when there are no other data

that suggest one of these is more likely than the others, we should choose the one in which derived traits evolve

the fewest number of times in the branches of the cladogram. Robusticity is a principle that states that trees that

maintain their basic form, even when different options are applied to the sequence of changes in one or more of

their branches are preferable. Obviously, parsimony and robusticity are only guiding principles. As more data

is made available, these principles are secondary to the picture afforded by that data. in determining which tree

is the best out of a series of possible alternatives.

Mr.

Bu

rris

: A

P B

iolo

gy

AP Biology: Unit 7: Evolution Pod 2: Phylogeny

Unit 7: Activity 7.11 - Adapted by D. Knuffke from Scientific Argumentation In Biology: 30 Classroom Activities by V. Sampson and S. Schleigh

Copyright 2013 by the National Science Teachers Association. www.nsta.org/store

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