SOLUTION: Let Build a Cladogram Teacher Guide - Studypool - Free Printable

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🔍 Understanding the Task: Let's Build a Cladogram!

A cladogram is a diagram that shows the evolutionary relationships among organisms based on shared derived characteristics (also called synapomorphies). The goal is to group organisms by their common traits, starting from the most ancestral (outgroup) to the most derived.

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✔ Step 1: Identify the Outgroup

From the guide:

> 6. The out-group in your data table is the: lamprey

✔ Why?
The lamprey lacks all derived traits (all “-” values), so it’s the most primitive organism here and serves as the outgroup—a reference point to determine which traits are derived (new) versus ancestral.

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✔ Step 2: Analyze Derived Characters

We look at each trait and see which organisms have it (+). These are derived characters that evolved in certain lineages.

| Character | Organisms with Trait |
|---------|----------------------|
| Jaws | Trout, Caecilian, Turtle, Cat, Gorilla, Human |
| Limbs | Turtle, Cat, Gorilla, Human |
| Hair | Cat, Gorilla, Human |
| Lungs | Caecilian, Turtle, Cat, Gorilla, Human |
| Opposable thumb | Gorilla, Human |
| Upright posture | Human |

Note: Jaws is the most common derived trait — present in 6 out of 7 organisms (all except lamprey).

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✔ Step 3: Answer Given Questions

#### c) The most common derived character is: jaws
✔ Correct. Jaws appear in 6 organisms, more than any other trait.

#### f) Which organism has only one shared derived character? trout
Let’s check trout:
- Jaws: + ✔
- Limbs: - ✘
- Hair: - ✘
- Lungs: - ✘
- Opposable thumb: - ✘
- Upright posture: - ✘

➡️ Only jaws → 1 derived character

✔ So, trout has only one shared derived character.

#### g) Which organism has two shared derived characters? caecilian
Check caecilian:
- Jaws: + ✔
- Limbs: - ✘
- Hair: - ✘
- Lungs: + ✔
- Opposable thumb: - ✘
- Upright posture: - ✘

→ Jaws and lungs → 2 derived characters

✔ So, caecilian has two.

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🧩 Step 4: Build the Cladogram (Conceptual)

We now build the cladogram by grouping organisms based on shared derived traits.

Start with the outgroup: Lamprey (no derived traits)

Then add organisms based on when new traits appear.

#### Order of Evolutionary Steps:

1. Jaws → first trait after lamprey
- Trout has only jaws → branches off early
- Others: Caecilian, Turtle, Cat, Gorilla, Human → also have jaws

2. Lungs → appears in Caecilian, Turtle, Cat, Gorilla, Human
- But Caecilian has lungs but no limbs/hair → may be a separate branch
- Turtle has limbs and lungs → shares with mammals
- Cat, Gorilla, Human share hair, lungs, etc.

3. Limbs → Turtle, Cat, Gorilla, Human
- Turtle has limbs but not hair → splits earlier
- Cat, Gorilla, Human → all have limbs and hair

4. Hair → Cat, Gorilla, Human → mammal clade

5. Opposable thumb → Gorilla, Human

6. Upright posture → Human only

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🌲 Cladogram Structure (Text-Based Representation)

```
┌── Lamprey
│
├───┬── Trout (jaws)
│ │
│ └── Caecilian (jaws, lungs)
│
└────┬── Turtle (jaws, limbs, lungs)
│
└───┬── Cat (jaws, limbs, hair, lungs)
│
└───┬── Gorilla (jaws, limbs, hair, lungs, opposable thumb)
│
└── Human (jaws, limbs, hair, lungs, opposable thumb, upright posture)
```

> Note: This is a simplified version. In reality, caecilian might be grouped with amphibians, and turtle with reptiles, but this exercise focuses on traits.

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✔ Summary of Answers:

| Question | Answer | Explanation |
|--------|--------|-----------|
| Outgroup | Lamprey | Lacks all derived traits |
| Most common derived trait | Jaws | Present in 6 organisms |
| Organism with 1 derived trait | Trout | Only has jaws |
| Organism with 2 derived traits | Caecilian | Has jaws and lungs |

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📝 Teacher Tips Recap:

- Print images in color if possible; laminate for reuse.
- Students work in pairs but complete their own handouts.
- Use the data table to identify shared derived traits.
- Start cladogram with outgroup (lamprey).
- Add branches based on appearance of new traits.

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✔ Final Answer Key (for students):

> 6. Outgroup: lamprey
> 7c. Most common derived character: jaws
> 7f. One shared derived character: trout
> 7g. Two shared derived characters: caecilian

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If you need me to draw the actual cladogram (as a visual), let me know—I can describe how to draw it or provide a textual version with proper branching.