Reading Evolutionary Trees — Practice · Grade 10 Science

Chapter: Evolution, Ancestry & Biodiversity

What this practice covers

By the end of Reading Evolutionary Trees you should be able to:

8 questions, multiple choice and written answer, each with a worked explanation.

Vocabulary used: node, sister lineages, derived feature.

Problem 1

On ((A,B),C), which are sister lineages?
  1. A and B
  2. A and C
  3. B and C
  4. Every pair equally
Answer and explanation

A and B

A and B share the most recent node.

Problem 2

Why should an unlabeled branch length not be read as time?
Answer and explanation

The diagram has not defined a time scale; length may be purely a layout choice.

Problem 3

Why can a shared function fail to show closest ancestry?
Answer and explanation

Similar functions can evolve independently; multiple traits and sequence evidence help test relationships.

Problem 4

In a tree, A and B share a recent node; C joins their branch at an older node. Which pair is most closely related? Explain the reasoning in your own words.
Answer and explanation

A and B are the closest pair in the supplied tree.

Trace the shared ancestors rather than the page spacing.

A and B share the most recent node.

Response criteria

  • Use the stated conditions.
  • Show the evidence or calculation.
  • Explain the conclusion and any stated limitation.

Problem 5

If branches rotate around a node, does common ancestry change? Show the reasoning, not just the conclusion.
Hints

A tree's topology carries relatedness; lengths need a declared scale.

Answer and explanation

No. The same branching connections remain.

Problem 6

Without a time scale, can a long branch be assumed to mean twice as many years?
Hints

State what the supplied observations or conditions establish, and separate that from any assumption.

Answer and explanation

No. Branch length represents time only when the diagram specifies that convention and scale.

Problem 7

A relationship tree does not imply an unstated time scaleA relationship tree does not imply an unstated time scaleABCNo time scale shownNo “progress” rankingNo ancestral tip assumedOnly specified branch metrics can support distance or time comparisons.
Original unscaled cladogram; distances and node positions are intentionally not numerical age evidence.
Interpret the supplied visual. Can this arbitrary-length tree tell when A and B diverged?
Answer and explanation

No. A dated or otherwise calibrated model and uncertainty are needed; topology alone supplies relative relationships.

A branch metric may represent elapsed time, genetic change or another quantity when explicitly defined. Many classroom cladograms show topology only, so drawn horizontal distance cannot establish divergence dates or which lineage changed fastest. Missing lineages and unresolved nodes also limit interpretation. A long branch on an unscaled diagram is not evidence of greater complexity, age or survival value. Read the legend, rooting and sampling before attempting any quantitative relationship comparison.

No. A dated or otherwise calibrated model and uncertainty are needed; topology alone supplies relative relationships.

Response criteria

  • Read the structures, axes, directions and units correctly.
  • Connect the evidence with the biological mechanism.
  • Respect stated model assumptions and distinguish an observation from a further inference.

Problem 8

A rooted tree has topology ((A,B),C). A drawing is rotated to show B first, then A, then C. State the relationship and explain what is needed to estimate divergence time.
Answer and explanation

A and B remain sister lineages in that topology. Tip order does not alter their shared ancestor; time estimation needs a specified calibrated branch metric/model and uncertainty.

A and B remain sister lineages in that topology. Tip order does not alter their shared ancestor; time estimation needs a specified calibrated branch metric/model and uncertainty.

Response criteria

  • Use the stated measurements or conditions, with correct units.
  • Connect the result to the biological mechanism or evidence relationship.
  • Identify the assumption, model limit or further evidence requested.

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