The Wnt/beta-catenin Master Switch, How a Face Cell Decides What NOT to Be
Developmental domain · Lesson 12 of 20 · Principles of Biomedical Science (PBS)
Today's goal: Explain that Wnt/beta-catenin signaling tells a cranial cell to become bone or skin by actively repressing the default cartilage program, and predict the fate switch when that signal is lost.
What a finished product looks like
This is a model of the work you should turn in. Use it to check your own: match the structure and the level of detail, do not copy it. Your wording should be your own.
Decision tree (one cranial mesenchyme cell at ~E11.5):
- Wnt/beta-catenin ON: the cartilage program (Sox9) is switched OFF, so the cell becomes bone (osteoblast) or skin (dermal fibroblast).
- Wnt/beta-catenin OFF: the brake on cartilage releases, so the cell follows its default and becomes cartilage (chondrocyte), even where bone belonged.
Caption: The Wnt master switch matters because it tells a cell what NOT to become. Its main job is repression of the default cartilage fate, not a direct command to become bone (PMID:24586192).
How this was built, step by step
The finished product above did not appear all at once. Here is the path from the question to the turned-in work, so you can follow the same steps.
- 1Start from today's question: How does a single cranial cell decide whether to become bone, skin, or , and what is the off choice it has to actively avoid?
- 2Work the Model and the Explore questions to reason it out before writing anything.
- 3Pull the specific evidence the product needs from the reading and any database you used.
- 4Write it up in the required format: Draw a decision tree for one cranial cell with two branches. Label the branch taken when Wnt is ON (bone or skin) and the branch taken when Wnt is OFF (, the default). In one sentence, finish this idea: "The Wnt master switch matters because it tells a cell what ____."
- 5Check it against the rubric, then submit.
| Criterion | Proficient | Developing | Beginning |
|---|---|---|---|
| Complete | Every required part of the artifact is present and filled in. | Most parts are present, but one is missing or left blank. | Several parts are missing. |
| Accurate | The science and data are correct and match the evidence. | Mostly correct, with a small factual slip. | Key science or data is wrong. |
| Scientific reasoning (CER) | States a claim, backs it with specific evidence, and explains the reasoning. | Has a claim and evidence, but the reasoning is thin or missing. | Gives an answer with no evidence or reasoning. |
| Professional communication | Clear, organized, and labeled the way a clinician or scientist would write it. | Readable but disorganized or missing labels. | Hard to follow. |
| Submitted | Turned in the right way (Schoology for routine work) and confirmed. | Turned in, but in the wrong place or unconfirmed. | Not turned in. |
- CompleteProficient: Nothing is left blank: the model fills every part of "Draw a decision tree for one cranial cell with two branches. Label the branch taken when Wnt is ON (bone or skin) and the branch taken when Wnt is OFF (cartilage, the default). In one sentence, finish this idea: "The Wnt master switch matters because it tells a cell what ____."".
- AccurateProficient: Every number and claim matches the case evidence.
- Scientific reasoning (CER)Proficient: It names a claim, cites the specific evidence, and explains the reasoning, not just the answer.
- Professional communicationProficient: It is organized and labeled like a real chart note.
- SubmittedProficient: It would be turned in on Schoology and confirmed.
WebXam problem for today's skill
One exam-style question that uses exactly what you practiced today. Try it before you reveal the answer, then read why each choice is right or wrong.
Tap an answer to see the full explanation. Nothing is recorded or graded.