Why Is CL/P More Common in Some Groups?
Genetics domain · Lesson 16 of 20 · Medical Interventions (MI), with PBS overlap
Today's goal: Explain how allele frequency, ancestry, gene-environment interaction, and a liability threshold combine to make CL/P more common in some populations, and why a risk score built in one group transfers poorly to another.
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.
Recommendation: Do not sign off this European-built risk score for global clinical use yet.
- Evidence 1: rs987525 on 8q24 has a strong effect in Europeans (odds ratio about 2.57 per copy) but shows no evidence of association in Native-American-ancestry Guatemalan families.
- Evidence 2: rs642961 near IRF6 is a clear risk allele in Europeans but fails to replicate in African-ancestry Brazilian samples, where a different IRF6 SNP carries the signal.
- Reasoning: Allele frequencies and effect sizes differ by ancestry, so a score built on European variants is miscalibrated elsewhere and would over- or under-predict.
- What I would need first: well-powered association data and validated effect sizes in each target population before the score could be trusted there.
Worked Claim, Evidence, Reasoning (from the database)
Here is the whole reasoning move done once, on the same kind of evidence you will pull from the tool. Read how the claim, the actual value from the database, and the reasoning fit together, then write your own the same way.
- C
Claim. The rs642961 risk allele has different frequencies across ancestry groups, so its contribution to cleft risk cannot be assumed equal everywhere.
- EEvidence (what the tool actually showed). gnomAD, rs642961 populations breakdown: the risk allele is least common in African-ancestry samples (about 0.11) and most common in Native American samples (about 0.27), with European samples in between.
- R
Reasoning (from the result to the inference). If one risk allele is more than twice as common in one group as in another, then a risk score that simply adds up that allele will weigh it differently depending on whose genome you score. A model trained where the allele is common will misjudge a population where it is rare. The frequency split read straight from gnomAD is direct evidence that risk variants are ancestry-dependent, which is exactly why a single-ancestry polygenic score should not be applied unchanged to everyone.
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: Why is lip and/or far more common in some human populations than in others?
- 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: A research consortium hands you a draft polygenic risk score for CL/P built entirely from European data and asks you to sign off for global clinical use. In three to four sentences, give your recommendation and cite at least two pieces of evidence (for example the 8q24 non-replication in Guatemalan families and the rs642961 non-replication in African-ancestry samples), then say what data you would need before the score could be trusted in a new population.
- 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 "A research consortium hands you a draft polygenic risk score for CL/P built entirely from European data and asks you to sign off for global clinical use. In three to four sentences, give your recommendation and cite at least two pieces of evidence (for example the 8q24 non-replication in Guatemalan families and the rs642961 non-replication in African-ancestry samples), then say what data you would need before the score could be trusted in a new population.".
- 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.