Read the branching history.

Phylogenetic trees represent hypotheses about evolutionary relationships. A node marks a common ancestor; taxa sharing a more recent node are more closely related in the represented history.

DNA sequences and morphological traits can both provide evidence. Rotating branches around a node does not change relationships. Horizontal distance on a simple cladogram does not necessarily show time unless a scale is supplied.

INTERACTIVE MODEL

Shared traits and ancestry

Trait 1 occurs in B and C; their most recent common node groups themTrait evidenceTrait 1Trait 1Trait 3

Explore: Switch between trait datasets and see how shared traits group taxa.

\text{shared derived traits}\to\text{branching hypothesis}

WORKED EXAMPLE

Taxa B and C share a node after their lineage splits from A.

B and C share a more recent common ancestor with each other.
Their left-to-right drawing order alone is not the evidence.

Assumed knowledge

Inheritance and variation.

Learning checkpoints & source

YOUR LEARNING CHECKPOINT

Identify a common ancestor on a tree.
Use shared derived traits to infer relationships.

QCAA Biology · Unit 4 · Continuity of life on Earth ↗

READY TO TRY IT?

Read the branching history.

Shared traits and ancestry

Taxa B and C share a node after their lineage splits from A.

Put the idea to work.