This is a working draft for Leslie's review. The dependency edges below are a first pass — the diagram and the prerequisite table are the parts to check hardest, since they drive hold-vs-advance decisions.
The course map shows the eight units as a spine — tools and ethics first, comparative anatomy last. But the real prerequisite structure isn't a straight line: it's a directed graph. Dissection skills are more strictly cumulative than most subjects — the earthworm needs safe handling and clean incision, the grasshopper needs the earthworm's careful method, and the vertebrates build on every invertebrate that came before. A weak skill early doesn't just lower one grade, it cascades into everything downstream that needs it. This page is the map a guide uses to find the skill that's actually blocking a stuck student.
An arrow means “must be mastered first.” Units 05, 06, and 08 each pull from two upstream units — those are the cascade points where one soft prerequisite quietly breaks several later units.
Prerequisite gating
A unit unlocks when its prerequisites are mastered — demonstrated, not merely seen. "Covered in class" is not the gate; a cleared rubric is. The difference matters most at the cascade points, where a soft prerequisite quietly breaks two or three later units.
| Unit | Must have mastered first |
|---|---|
| 01 Tools, Safety & Ethics | — (entry point) |
| 02 Earthworm | 01 (safe handling and clean incision before any specimen) |
| 03 Grasshopper | 02 (the earthworm's careful-incision method carries to the first arthropod) |
| 04 Clam or Squid | 02 (soft-body dissection extends the earthworm's careful incision) |
| 05 Perch | 03 (invertebrate internal survey) + 04 (soft-body handling) — the first vertebrate synthesizes both |
| 06 Frog | 03 (arthropod system survey) + 05 (the vertebrate body plan) |
| 07 Fetal Pig | 05 (the vertebrate body plan, scaled up to a mammal) |
| 08 Comparative Anatomy | 06 (amphibian organ systems) + 07 (mammalian organ systems) |
Gap-cascade diagnosis
When a student stalls late, the visible symptom is rarely the real problem — the broken concept is usually upstream. Trace the arrows backward. Common cascades:
| Late symptom | Upstream concept to check first |
|---|---|
| Comparative anatomy homologies don't line up (Unit 08) | The vertebrate body plan from Unit 05 (Perch) — you can't compare organ systems you never learned to trace cleanly. |
| Frog organ-system tracing goes wrong (Unit 06) | The perch's vertebrate survey from Unit 05 — the frog's systems sit on the body plan the perch established. |
| Fetal-pig structure ID stalls (Unit 07) | The vertebrate body plan from Unit 05 (Perch) — the mammal is that plan scaled up, not a fresh start. |
| The perch comes apart before the survey (Unit 05) | The invertebrate incision technique from Units 03–04 — the specimen was damaged at the first cut. |
Using the graph to plan a re-attempt
The graph turns a "not yet" into a targeted re-attempt instead of a whole-unit re-teach. When a student fails a downstream demonstration:
- Trace backward to the upstream node the symptom points to.
- Re-attempt the upstream concept first — close the gap at its source, not where it surfaced.
- Then re-run the downstream demonstration. Often it passes without any re-teaching of the downstream unit at all, because the cascade is resolved.
This is also where the integration guide matters: some dissection skills depend on an applied idea — proportional reasoning for a scaled diagram, careful measurement for organ dimensions — from another spoke. When the upstream dissection node looks solid but the student still stalls, check the cross-disciplinary dependency before re-teaching the dissection.