Phylogeny Construction Protocol

From evidence to tree — how to build a cladogram, not just read one

Six pages on building cladograms from character matrices, DNA sequences, and distance matrices — what AP actually tests under CED 7.9 and Skill 2.D. Covers the molecular-over-morphology rule and Q5 placement traps.

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Exam Weight

Q5 · 4 pts

MCQs

1–2 placement

FRQ Appearance

Q3 · Q5

Sprint Time

~25 min

Quick Glance — all topics in this unit

Priority, exam format, and the trap that most often costs the point. Transcribed from page 1 so this content is searchable.

Topic	Priority	Format	Key trap / must-know
P1 Reading vs. Constructing	★★★	Q5	S8 covered reading; Q5 also asks you to BUILD trees from data.
P2 Three Construction Rules	★★★	All trees	Outgroup first, derived (not ancestral) traits, mark each trait at its first-appearance branch.
P3 Method A — Character Matrix	★★★	Q5	Rank by # derived traits; build outward from outgroup, not by row order.
P4 Method B — DNA Sequence	★★★	Q5	Smallest pairwise difference = sister taxa; molecular > morphology when they conflict.
P5 Method C + Construction Traps	★★	Q5	Don't draw by row order, don't use ancestral traits, don't put modern taxa at internal nodes.
P6 Practice + Cheat Card	★★	Q5	Use 'derived/ancestral' — never 'more evolved' or 'more primitive'.

Topic-by-topic visual review

Nine pages, one topic each. Open the PDF for print quality, or scroll to study on screen.

Cover for AP Biology FRQ Q5 phylogeny construction playbook. From Evidence to Tree: how to build a cladogram, not just read one. Module covers character matrix to cladogram, DNA sequence to tree, and distance matrix to tree. Tags: Unit 7, Skill 2.D, Q5 prep, construction-focused. — **Cover** · Phylogeny construction protocol — from raw data to cladogram. CED 7.9 / Skill 2.D / Q5 prep.

Three universal rules for phylogeny construction. Rule 1 outgroup first: most distantly related taxon, fewest derived traits, defines the root. Rule 2 use synapomorphies (shared derived traits) not symplesiomorphies (shared ancestral traits) to define clades. Rule 3 place each derived trait at the branch where it first appears in evolutionary history. — **Three Universal Construction Rules** · Outgroup first · Use shared derived (not ancestral) traits · Place each trait at its first-appearance branch.

Method A character matrix to cladogram. Five-step protocol: identify outgroup, count derived traits per taxon, find shared derived traits, build branches outward from outgroup, mark each trait at first-appearance branch. Worked example shows lancelet, lamprey, frog, platypus, mouse with vertebrae, lungs, hair, placenta traits, building (((Mouse, Platypus), Frog), Lamprey, Lancelet) topology. — **Method A — Character Matrix → Cladogram** · Five-step protocol with vertebrate worked example. Rank taxa by number of derived traits.

Method B DNA or protein sequence to tree. Four-step protocol: calculate pairwise differences, find smallest difference for sister taxa, build outward, apply molecular over morphology rule. Worked example with four species, eight nucleotide region, pairwise differences matrix, ((Sp1, Sp2), (Sp3, Sp4)) topology. Molecular versus morphology callout: bats and birds have wings (convergent), DNA tells the real story. — **Method B — DNA / Protein Sequence → Tree** · Smallest pairwise difference = sister taxa. When molecular and morphological data conflict, molecular wins.

Method C distance matrix to tree, plus construction-specific traps. Distance matrix protocol: smallest distance equals sister taxa, recompute with averaging, repeat. Traps include drawing by table row order, using shared ancestral traits to define a clade, letting morphology override molecular data, drawing internal-node ancestors as living species, using 'more evolved' or 'more primitive' language. — **Method C + Construction Traps** · Distance matrix protocol plus the five most common Q5 construction errors students make.

Practice questions and one-page cheat card. MCQ practice: choosing tree topology from a character matrix. Q5-style FRQ: salamander pairwise differences, evaluating a coloration-based claim using molecular data. Cheat card: three methods (character matrix, DNA sequence, distance matrix) shown side by side with the four steps for each method. Universal rule: smaller sequence difference or distance equals more recent common ancestor. — **Practice + One-Page Cheat Card** · MCQ + Q5-style FRQ practice with model answers, plus a side-by-side cheat card across the three construction methods.

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