Clue 1: Orient yourself
Which model can test load?
Use the labels and the picture's left-to-right, near-to-far, or before-and-after order. Name only what you can point to.
The question
When can a mouse answer a question about a human face, and where does the comparison stop?
Why it matters: Clinical recommendations affect real children and families. Fair comparisons, bias control, ethical limits, and honest uncertainty keep a promising result from becoming a harmful claim. Today you practice the professional reasoning behind that work: A model earns relevance by matching the mechanism and outcome needed for the question while following Replace, Reduce, and Refine.
On your WebXam
Distinguishing construct validity from face validity in an animal model
For life
To find the cause, change one thing and watch what changes.
Principle: Same look, different cause
Five principles we return to
Having it is not using it
Same instructions, different switches
Same look, different cause
Change one thing and watch
Boss or doorman?
Decides the result or only allows it
Held down, not gone
Remove the brake and it returns
Many roads, one ending
One result can begin many ways
Try the everyday version first
A scale model is useful only for the feature being tested
A scale model copies selected features of a larger system. It can answer questions about those features, but not about details the model leaves out.
Do not jump to the biology yet. Treat the picture as a small system. Track its parts, follow one change at a time, and keep more than one explanation open until the picture supplies a way to separate them.
Clue 2: Trace one change
Which model only matches appearance?
Follow one object, stage, or path. Point to the first place where the situation changes instead of jumping to the ending.
Clue 3: Keep the cause open
What question could be answered without a whole animal?
List more than one explanation that still fits. Name the extra observation that would help you separate those possibilities.
Now inspect the illustration
Work from the visible evidence. A useful answer names the part of the picture that supports it and leaves unknown causes open.
- 1Which model can test load?
- 2Which model only matches appearance?
- 3What question could be answered without a whole animal?
Tier 1 check
Finish with the everyday model
Use the everyday picture to answer today's question in plain words: When can a mouse answer a question about a human face, and where does the comparison stop?
You can complete today's required check without opening the technical details below.
Ready for the real names? Optional tier 2
Technical rules and limits
Rule 1: Define the exact mechanism and outcome the model must reproduce.
Rule 2: Use the least sentient suitable system.
Rule 3: Replace, Reduce, and Refine animal use while preserving a valid answer.
Where the analogy stops: Living models can share pathways without copying every feature of human development or care.
Carry the previous idea forward
CRISPR is a controlled perturbation only when the edit, mosaicism, phenotype, and off-target controls are verified.
Today's technical takeaway
A model earns relevance by matching the mechanism and outcome needed for the question while following Replace, Reduce, and Refine.
Now map the same rules onto biology
Select a model for palatal shelf elevation
Feature under test
Construct and functional relevance
Visible similarity
Face validity
Least burdensome model
Replace, Reduce, Refine
Educational illustration, not a clinical photograph or a patient-specific study plan. Use the supplied evidence cards and claim ceiling.
Mateo's case file: evidence supplied in this lesson
EXP11-E1
The question asks whether a pathway changes mammalian palatal shelf elevation and fusion.
Why it matters: A model must represent the relevant tissue movement and timing.
EXP11-E2
A cell culture can test signaling but cannot reproduce whole-palate elevation.
Why it matters: It can replace animals for some early questions, not the full outcome.
EXP11-E3
A mouse study uses prior data for sample size, shared controls, analgesia, humane endpoints, and blinded scoring.
Why it matters: The design applies Reduce and Refine while protecting validity.
Make the clinical decision
You are the model-selection and animal-welfare reviewer.
The team wants to use the largest animal available because it seems more human-like.
AChoose the least burdensome model that can measure the required mechanism and outcome.
BChoose by body size alone.
CReject all nonhuman and cell models as useless.
Choose the model sequence and justify it with mechanism fit plus the 3Rs.
Evidence required
EXP11-E1 + EXP11-E2 Claim ceiling
You may judge fitness for the stated question. You may not call any model a complete stand-in for Mateo.Go deeper Optional tier 3
Everything required for today is above. Open these only if you want the explainer, source trail, or download files.
The everyday model and Tier 1 check are the complete required path for this lesson.
Use these checks to keep your place. They are not turned in through the portal.
Check off as you finish
- Worked through the everyday picture and answered its three questions.
- Completed the Tier 1 check in plain words.
Turn in: Experimental Design lesson 11: When Is a Mouse a Good Stand-In for Mateo?
Go to Schoology to turn this in.
Submit one PDF. Put your first and last name in the document header. Name the file: FirstName LastName - Assignment Title - YYYY-MM-DD.pdf.
Open Schoology PDF upload helpIf you cannot get in, see Mr. Mendoza. Do not skip the work.
Optional legacy technical materials Open only if you want the original notes, vocabulary, artifact, and CER work
Before this page, you should know
- is programmable: a guide RNA matches a chosen and directs the Cas9 to cut there, and the cell's repair can be steered to knock a gene out, knock one in, or install a single point .
- To target a new site you only redesign the guide RNA, not rebuild a whole animal, so is far faster than older methods.
If not, review
Today's new idea is only
A model is judged on two separate kinds of good: whether it breaks the same cause () and whether it looks like the disease (), and animal work is governed by .
Goal: Judge a proposed mouse study by and , and apply (Replacement, Reduction, Refinement) and ARRIVE reporting to decide whether the model can honestly answer a human question.
Know by the end
- An is a non-human organism studied to learn about a human condition; it is a stand-in, never the disease itself.
- asks whether the model disrupts the same cause (gene or pathway) believed to act in humans; asks whether the model looks like the human disease.
- Penetrance is the percent of mutant animals that actually show the phenotype; in the real Ezh2 study only about 20% of mutant mice were born with a .
- (Replacement, Reduction, Refinement) and the govern and report animal research; Reduction is a statistics and power idea, not only a kindness idea.
1
Two kinds of good, named
Model start: A model is never the disease itself, so we judge how trustworthy the stand-in is on two separate axes, not one.
- asks whether the model breaks the same ____ (gene or pathway) we think acts in humans.
- asks whether the model ____ like the human disease, an actual you can see.
- In the Ezh2 study only about 20% of mutants showed a , which ____ (lowers / raises) the , and is exactly why scientists report the penetrance instead of pretending every animal clefts.
2
The 3Rs and ARRIVE
- Replacement: use a non-animal method (cells, computer models) when it can answer the question ____ animals.
- Reduction: use the ____ number of animals that still gives a valid answer; this connects directly to sample-size and power planning.
- ARRIVE exists because audits found randomization reported in only 30 to 40% of animal papers and sample-size justification in under ____ %.
Everything you need for today is on this page. These links are optional.
What to read
Read the short plain-language explanation written for this lesson. Plain-language explainer for this lesson
Why this source matters
This explanation gives you the background for today's idea without making you decode a research paper: A model is judged on two separate kinds of good: whether it breaks the same cause () and whether it looks like the disease (), and animal work is governed by .
Words to unlock first
animal modelface validityconstruct validitythe 3RsARRIVE guidelines
Reading moves
- Skim the title and abstract first to get the gist.
- Circle the one sentence that states the main claim.
- Box the evidence the authors give for that claim.
- Mark one sentence that confuses you, and move on.
Stop point
Stop after the final 'Use it now' section. The research citations are available separately for advanced readers.
Your output
Write one claim-evidence sentence: state the main idea, then name the example or evidence that supports it.
Where this fits
Tested on (Ohio WebXam)
Genetics of Disease · 072130
PLTW lesson
MI · Experimental Design domain · Model design and validity; the 3Rs and ARRIVE reporting in animal research
WebXam domain
Molecular and Genetic Technology
Evidence to produce
A junior researcher proposes: knock out a human cleft-pathway gene in 200 mice and see if they cleft. As PI, write three short notes back: (1) Validity: does this aim for construct validity, face validity, or both, and what is your evidence? (2) The 3Rs: name one R this proposal ignores and how to fix it (hint: where did 200 come from?). (3) Mateo link: if 20% of these mice cleft, what could you and could you not claim about a real human like Mateo?
Lab / skill
Biomedical Innovations (BI) · AP Biology
Everything required for today's decision is already in the case file and plain-language explainer. The links below are original papers and database records for teachers and advanced readers, not assigned student reading.
- Claim: A mouse (is / is not) a reasonable starting model for studying how Mateo's formed.
- Evidence: Cite one fact about the shared script and one fact about the ____ % penetrance in the Ezh2 study.
- Reasoning: Explain how and together support your claim, and name one limitation the partial penetrance forces you to admit.
How this is graded (rubric)
For: A junior researcher proposes: knock out a human cleft-pathway gene in 200 mice and see if they cleft. As PI, write three short notes back: (1) Validity: does this aim for construct validity, face validity, or both, and what is your evidence? (2) The 3Rs: name one R this proposal ignores and how to fix it (hint: where did 200 come from?). (3) Mateo link: if 20% of these mice cleft, what could you and could you not claim about a real human like Mateo?
| 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 through the route named under Submit here and confirmed. | Turned in, but in the wrong place or unconfirmed. | Not turned in. |
How the model answer scores against this rubric
- CompleteProficient: Nothing is left blank: the model fills every part of "A junior researcher proposes: knock out a human cleft-pathway gene in 200 mice and see if they cleft. As PI, write three short notes back: (1) Validity: does this aim for construct validity, face validity, or both, and what is your evidence? (2) The 3Rs: name one R this proposal ignores and how to fix it (hint: where did 200 come from?). (3) Mateo link: if 20% of these mice cleft, what could you and could you not claim about a real human like Mateo?".
- 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 attached to your class form or handed in, and confirmed.
What's next: We decided a mouse can be a fair stand-in when its construct and hold up. But knocking out a gene and seeing a is not yet proof the gene caused it; something else changed by the same edit could be to blame. So next: how do we prove the gene itself, and nothing else, caused the cleft? We chase that next time.