Same DNA, Different Outcome
Developmental domain · Lesson 17 of 20 · Principles of Biomedical Science (PBS)
Today's goal: Describe how DNA methylation and microRNAs change gene activity without changing the DNA sequence, and use the second hit idea to explain why two embryos with the same risk allele can differ.
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.
Embryo 1: First hit = small inherited risk allele. No second hit. Total stays under the clefting threshold. Outcome: palate fuses normally.
Embryo 2: First hit = the same risk allele. Second hit = low folate plus higher CDH1 (E-cadherin) promoter methylation that quiets an adhesion gene. Total crosses the threshold. Outcome: cleft.
Why it fits an isolated cleft: A messy, additive picture where several small pushes must add up explains why family members with the same allele can differ (penetrance), which fits an isolated multifactorial cleft far better than a single all-or-nothing gene would (PMID:28550290).
This model shows the level of evidence and organization needed to complete: A first-hit / second-hit threshold diagram that explains incomplete penetrance.
- Date and label the entry.
- Record the procedure, observation, or design decision clearly.
- End with what the evidence means and the next step.
Keep the structure. Replace the question, facts, measurements, and evidence. Then recheck units, vocabulary, and whether the conclusion goes beyond the evidence.
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: What stays the same in both performances?
- 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: Build a two-embryos diagram. Both carry the same small . 1 stays under the threshold and the fuses. Embryo 2 picks up a (for example, low plus a methylation change quieting an gene) and crosses into clefting. Label the first hit, the second hit, and the outcome for each, then write one sentence on why this additive picture fits an better than a single-gene syndrome.
- 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 through the route named under Submit here 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 "Build a two-embryos diagram. Both carry the same small risk allele. Embryo 1 stays under the threshold and the palate fuses. Embryo 2 picks up a second hit (for example, low folate plus a methylation change quieting an adhesion gene) and crosses into clefting. Label the first hit, the second hit, and the outcome for each, then write one sentence on why this additive picture fits an isolated cleft better than a single-gene syndrome.".
- 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.
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.
It builds this reusable test skill: Using the second-hit model to explain incomplete penetrance.
- Name the concept or data pattern being tested.
- Cross out choices that violate that rule or the evidence.
- Justify the best remaining choice before checking the answer.