Read a branching relationship model

Supplied materials

• All measurements and observations below are supplied classroom examples. They are not data from actual learners or a claim about a particular real site.
• Paper or a browser document for a labeled drawing, table or explanation.
• Worked problem inputs: Tree pairs A with B at a recent node, while C is printed beside A. Which relationship matters?
• Assessment case 1: A tree joins A and B at one recent node; C joins earlier but is printed beside A. Which inference follows? Which inference or prediction is best supported?
• Assessment case 2: Which scientific label fits the specifically described step or feature? Supplied case: A and B share the newest shown node.
• Assessment case 3: Which scientific label fits the specifically described step or feature? Supplied case: Label appears at branch endpoint.
• Assessment case 4: Which scientific label fits the specifically described step or feature? Supplied case: Dashed relationship has insufficient evidence.
• Assessment case 5: Which scientific label fits the specifically described step or feature? Supplied case: Most recent shared branching point.
• Assessment case 6: A tree shows three branches from an unresolved node with no pairwise order. What follows? Which inference or prediction is best supported?

Learn the idea

A branching tree models common ancestors and lineages, not a ladder from inferior to superior. Nearby printed tips do not establish relationship; shared branching points do.

Common ancestor means branch point connecting lineages. Sister lineages means share the most recent modeled branch point. Tip means sampled lineage at branch end. Uncertain branch means relationship not resolved by supplied evidence.

For the supplied mechanism problem, Tree pairs A with B at a recent node, while C is printed beside A. Which relationship matters? The A–B shared branch point establishes their closer modeled ancestry. Printing C beside A does not change the branching relationship. Layout distance is not evolutionary relatedness.

1. Read the supplied problem and mark the structures, processes or quantities named: Tree pairs A with B at a recent node, while C is printed beside A. Which relationship matters?
2. Draw the relevant boundary, pathway or comparison and label it using the scientific ideas above.
3. Write a causal explanation or calculation, showing how each observation supports the result.
4. Compare your reasoning with the worked solution; name a condition that would change or limit the inference.

Check your reasoning

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Take it further

New tree task: node 1 splits C from a lineage; node 2 later splits that lineage into A and B. Expected: A and B share the more recent ancestor; redraw tip positions without changing the branching relationship.

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