Clue 1: Orient yourself
Which panel shows the exposure before the outcome?
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
Which panel shows the exposure before the outcome?
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: Cohorts establish time order, while twin comparisons estimate population patterns under assumptions rather than one person's cause.
On your WebXam
Interpreting twin concordance and what heritability does and does not mean
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 movie follows events forward while a matched split screen compares two paths
A movie preserves sequence, while a split screen compares two similar situations at the same time. Each view answers a different question about change.
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
What is more similar within one pair?
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
Which shared condition could make a pair look alike from birth?
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 panel shows the exposure before the outcome?
- 2What is more similar within one pair?
- 3Which shared condition could make a pair look alike from birth?
Tier 1 check
Finish with the everyday model
Use the everyday picture to answer today's question in plain words: Which panel shows the exposure before the outcome?
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 starting population before outcomes occur.
Rule 2: Measure exposure and follow-up consistently.
Rule 3: State the assumptions behind twin comparisons.
Where the analogy stops: People do not follow scripted film paths, and twins can share environments in unequal ways.
Carry the previous idea forward
Case-control studies efficiently study rare outcomes, but their odds ratios remain vulnerable to selection, recall, and confounding.
Today's technical takeaway
Cohorts establish time order, while twin comparisons estimate population patterns under assumptions rather than one person's cause.
Now map the same rules onto biology
Compare a prospective cohort with a twin concordance study
Forward film
Prospective cohort
Matched split screen
Twin comparison
Shared set
Shared genes and environment
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
EXP05-E1
A cohort records an exposure before birth outcomes are known.
Why it matters: This supports time order and reduces some recall problems.
EXP05-E2
Monozygotic twins share more DNA than dizygotic twins on average.
Why it matters: Higher concordance can support a genetic contribution at the population level.
EXP05-E3
Twin estimates rely on assumptions, and heritability changes across populations and settings.
Why it matters: The estimate does not assign a percentage cause to Mateo.
Make the clinical decision
You are selecting a design for a grant proposal on cleft risk.
The proposal claims a twin study can cleanly separate genes from environment for one infant.
AUse cohort and twin evidence with explicit assumptions and population-level wording.
BTreat twin concordance as a personal genetic diagnosis.
CIgnore shared environment because identical twins share DNA.
Choose the defensible claim and name one strength plus one assumption for each design.
Evidence required
EXP05-E1 + EXP05-E2 Claim ceiling
You may discuss time order and population variance. You may not assign Mateo's cleft a heritability percentage or single cause.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 5: Measuring Inheritance Over Time and in Twins
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
- A starts with the outcome (cases versus controls) and looks backward at the suspected exposure; it is the workhorse for a rare outcome like a (about 1 in 700 births).
- The is the odds of exposure in cases divided by the odds in controls; above 1 suggests a , equal to 1 means no association, below 1 means less common in cases.
If not, review
Today's new idea is only
A cohort follows exposure forward to outcome, and a uses identical versus fraternal concordance to estimate heritability without naming a single gene.
Goal: Students will explain how a follows exposure forward to outcome, how a compares identical and fraternal concordance to estimate heritability, and what high heritability does and does not tell us about a single gene.
Know by the end
- A starts with the exposure and follows people forward to the outcome; a prospective cohort records exposure before the outcome, so it is largely immune to .
- A compares identical (about 100 percent shared DNA) and fraternal (about 50 percent shared) concordance to estimate heritability, after confirming zygosity.
- For lip with or without cleft , identical concordance was 50 percent versus 8 percent in fraternal twins, giving heritability above 90 percent.
- High heritability says genes explain most of the variation in risk across a population; it does NOT name one gene and is compatible with many small-effect genes plus environment.
1
The forward design
Model start: A starts with exposure and follows forward; recording exposure first makes a prospective cohort largely immune to .
- A starts with the ____ (exposure) and follows people forward in time to the outcome; a prospective cohort records exposure before the outcome exists, so it is largely immune to .
- Its native measure is the (RR): risk in the exposed group divided by risk in the unexposed group; the price is size and patience for a rare outcome.
2
Twins as nature's experiment
- A uses identical and fraternal twins to estimate heritability after confirming each pair's zygosity; the engine is concordance, how often the second twin is affected given the first one is.
- If identical concordance is much ____ (higher) than fraternal concordance, genes are doing the work; if the two are about equal, shared environment is. For clefting, 50 percent towered over 8 percent, giving heritability above 90 percent.
3
What heritability does NOT say
- High heritability says genes account for most of the variation in risk across the population; it does not say one gene is responsible or that a cleft is inherited in a simple pass-it-down pattern.
- A trait can be highly heritable and still depend on many genes each adding a little, plus environment; the 50 percent identical discordance shows non-genetic factors still operate.
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 cohort follows exposure forward to outcome, and a uses identical versus fraternal concordance to estimate heritability without naming a single gene.
Words to unlock first
cohort studyprospectiverelative risktwin studyconcordance
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 · Epidemiology, cohort and twin designs, and heritability
WebXam domain
Molecular and Genetic Technology
Evidence to produce
Present the twin result at the team meeting: state the identical and fraternal concordances and which is higher, explain in one sentence why this points to genes rather than the shared womb, and answer in two sentences whether heritability above 90 percent means Mateo's future siblings will almost certainly have a cleft.
Lab / skill
Biomedical Innovations (BI) · Medical Interventions (MI)
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.
- STROBE. Reporting guidance for observational studies.
- Grosen D, et al. 2011. Risk of Oral Clefts in Twins. Epidemiology. [PMID:21423016]
- Sun B, et al. 2023. Ezh2-dependent methylation in oral epithelia promotes secondary palatogenesis (cleft prevalence about 1 in 700). Birth Defects Res. [PMID:37435868]
- Claim: Genes contribute strongly to risk.
- Evidence: The found identical concordance of ____ percent and fraternal concordance of ____ percent.
- Reasoning: The gap between those numbers is evidence for genes and not for shared environment, because both twin types share the womb equally, so the main thing that differs is how much ____ they share.
How this is graded (rubric)
For: Present the twin result at the team meeting: state the identical and fraternal concordances and which is higher, explain in one sentence why this points to genes rather than the shared womb, and answer in two sentences whether heritability above 90 percent means Mateo's future siblings will almost certainly have a cleft.
| 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 "Present the twin result at the team meeting: state the identical and fraternal concordances and which is higher, explain in one sentence why this points to genes rather than the shared womb, and answer in two sentences whether heritability above 90 percent means Mateo's future siblings will almost certainly have a cleft.".
- 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: The tells us genes carry most of the risk, but heritability is just a number; it does not name a single gene. Out of roughly twenty thousand genes, how do scientists track down the specific risk gene hiding among millions of bases?