AP Biology Unit 7 Topic 4: Phylogeny

What to Know

Branch points represent common ancestors, not modern organisms turning into one another.
Shared derived characters are especially useful for grouping related lineages.
Molecular and morphological evidence can support or revise phylogenetic hypotheses.
Always connect this topic back to the larger unit: Natural Selection.

Detailed Notes

Phylogeny belongs to Unit 7: Natural Selection. Phylogenies are models of evolutionary relationships built from shared traits and tested with evidence. Treat the topic as a relationship between structure, process, evidence, and biological function instead of memorizing an isolated definition.

Key relationships: Branch points represent common ancestors, not modern organisms turning into one another. Shared derived characters are especially useful for grouping related lineages. Molecular and morphological evidence can support or revise phylogenetic hypotheses.

Model to use: Read a cladogram by identifying common ancestors, sister groups, derived characters, and the outgroup. A clear model should label the parts, show the direction of movement or information flow when relevant, and connect the diagram back to the biological outcome.

AP-style move: When comparing trees, focus on branching order and shared ancestry, not the left-to-right order of tips. Strong answers name the concept, apply it to the scenario, and explain the reasoning in complete sentences.

Key Vocabulary

Phylogenetic tree

A branching model showing hypothesized evolutionary relationships.

Clade

A group containing an ancestor and all of its descendants.

Derived character

A trait that evolved in a lineage and helps define groups.

Outgroup

A comparison lineage used to infer ancestral and derived traits.

Monophyletic group

A group that includes one ancestor and all descendants of that ancestor.

Parsimony

A reasoning approach that favors the simplest explanation consistent with evidence.

Quick Practice

How would you explain Phylogeny in one or two AP-style sentences?

Name the concept, apply it to a specific example or source, and explain the reasoning that connects the evidence to your answer.

Official Alignment

Reference and Attribution

Biology concept reference: Biology for AP Courses by OpenStax, Rice University. Access for free at OpenStax. Licensed under the Creative Commons Attribution-NonCommercial-ShareAlike 4.0 License. EduCompanion used this source as a conceptual reference and rewrote the study notes in original wording.