SNP and PTC case
This page has four parts, in the order you use them. Part 1 is what you need to know. Part 2 says what to do, in plain English. Part 3 shows the work done once on a case that is not yours. Part 4 is your own work and where to turn it in.
Open your materials, follow the steps, then turn in your work.
Connect a single-nucleotide polymorphism to a phenotype using the PTC-tasting genotype dataset.
Optional: listen or watch a unit review▸
Part 1 of 4 · Background and definitions▸
💡 Big idea: Three single-base differences in TAS2R38 are inherited together and change the shape of the bitter-taste , so that haplotype is what decides whether PTC tastes bitter or like nothing at all.
- • A is a single base-pair variation at a specific ; millions exist across the human genome.
- • The TAS2R38 gene carries three common SNPs that are inherited together as a haplotype; the PAV combination gives the taster phenotype and AVI gives the non-taster.
- • Inheriting at least one PAV haplotype usually gives the taster phenotype; two AVI haplotypes usually give the non-taster. Usually, not always: other genes and age shift it.
A pedigree is read by testing each inheritance pattern against every parent and child and keeping only the pattern that fits them all; a is someone the pattern forces to hold a hidden even though they show no trait.
Three single-base differences in TAS2R38 are inherited together and change the shape of the bitter-taste , so that haplotype is what decides whether PTC tastes bitter or like nothing at all.
Driving question: In the TAS2R38 dataset, why do some people gag on a PTC test strip while others taste nothing at all, when the classroom test reads one swapped nucleotide, one of the three that travel together?
What you already know: A pedigree is read by testing each inheritance pattern against every parent and child and keeping only the pattern that fits them all; a is someone the pattern forces to hold a hidden even though they show no trait.
New idea: Three single-base differences in TAS2R38 are inherited together and change the shape of the bitter-taste , so that haplotype is what decides whether PTC tastes bitter or like nothing at all.
Visual or model: No figure is attached to this lesson. The readings, the worked example and E1 to E3 carry the evidence.
- Observe or measure the relevant feature in today's lesson.
- Organize the observation with a stable evidence ID.
- Apply this rule: Stored information can be copied, read, and converted into a functional product.
- Choose the option the evidence supports and state the limit of the conclusion.
Real biomedical example: In the TAS2R38 dataset, why do some people gag on a PTC test strip while others taste nothing at all, when the classroom test reads one swapped nucleotide, one of the three that travel together?
What the evidence supports: E1 to E3 support the daily take-home when the response meets the stated success criteria.
What it cannot prove: The package does not support claims beyond this lesson's or any real patient diagnosis.
- • : One of the alternative versions of a gene found at the same spot on a , like the A, B, and O versions of the blood-group gene.
- • : The specific set of gene versions an individual carries, which works with the environment to shape observable traits.
- • phenotype: The observable traits of an organism, such as appearance or function, that result from its combined with environmental influences.
- • pedigree: A family tree drawn with standard symbols (squares for males, circles for females, filled for affected) so any geneticist can read a family at a glance.
- • : A single-nucleotide polymorphism, a one-letter difference in at a specific spot that varies between people.
- • : A person who carries one copy of a disease without showing symptoms but can pass it to their children.
- • : A guided conversation with a trained specialist who explains inherited disease risks, test options, and choices to help a family make informed decisions.
Use it now: Choose one decision option. Cite E1 and E3, then explain how the rule connects the evidence to your choice. This is thinking practice for the one turn-in named under Turn in, not a second submission.
Go further, optional: The source links below are optional enrichment. Every fact required for today's local evidence decision appears in this lesson package.
Genetic evidence can support an inheritance, , sequence, or expression explanation, but penetrance, regulation, environment, family structure, and test uncertainty can limit the conclusion.
Limit: A classroom , , pedigree, or molecular model does not establish a real person's diagnosis, prognosis, identity, or reproductive outcome.
Stored information can be copied, read, and converted into a functional product.
Limit: Genes are regulated biological sequences, not conscious instructions, and one gene rarely determines a whole trait alone.
You can read a and pair it to a phenotype.
Limit: E3 defines the classroom product or success criterion. It is not independent scientific evidence and cannot justify a clinical or causal claim.
Today's decision · Simulated classroom evidence scenario
Your role: medical interventions team member
Decision: Your team must decide what the evidence from today's lesson supports before submitting the labeled and result claim named on today's page.
- • Conclude that non-tasters are missing the taste gene, since a difference you can feel needs a big change.
- • Collect matching and taste results from a second, separate group before treating one letter as the whole story.
- • Explain the tasting difference as one assayed base in TAS2R38, part of a three-letter haplotype that alters the bitter taste .
Response: State one choice, cite at least two evidence IDs, explain the rule that connects them, and add one limitation. Use it inside the one turn-in named under Turn in; it is not a separate submission.
Claim ceiling: Today's evidence supports a classroom claim about today's lesson. It cannot prove causation, diagnose a real patient, or justify action outside this room.
Reason for review: Your team must decide what the evidence from today's lesson supports before submitting the labeled and result claim named on today's page.
Context: One base-pair change at the right spot can flip a phenotype, because a single nucleotide polymorphism can alter the a gene builds, and that is why individual letters, not just whole genes, matter for who we are.
- • T1: Open the teacher dataset (Activity 2.1.3 in myPLTW if it opens) and find the column for the PTC-tasting gene. If myPLTW will not open, use this practice readout at the one assayed position (C marks the PAV, taster, haplotype and G marks AVI): Person 1 CC, tastes PTC; Person 2 CG, tastes PTC; Person 3 GG, does not taste it.
- • T2: For three people, write their next to their phenotype and mark homozygous or heterozygous.
- • T3: Decide whether the tasting tracks with the trait and write one sentence of evidence.
- • T4: Predict the status of one labeled person using language.
- • T5: Submit your -to-phenotype table and prediction as your daily evidence.
- • E1: Genetic evidence can support an inheritance, , sequence, or expression explanation, but penetrance, regulation, environment, family structure, and test uncertainty can limit the conclusion.
- • E2: Stored information can be copied, read, and converted into a functional product.
- • E3: You can read a and pair it to a phenotype.
Measurements: No patient measurement is supplied unless it appears explicitly in E1-E3. Do not invent a value.
Uncertainty: This is a composite classroom scenario. Missing history, measurements, or confirmation tests remain unknown and limit the conclusion.
Students often think a non-taster must have 'no gene' for tasting, or that the difference is a large deletion, because they assume big phenotype differences require big differences. The trap: Both tasters and non-tasters have the TAS2R38 gene. The classroom readout tests a single base-pair swap (a ) at one of the three linked positions, not a missing gene. Expecting a huge change for a clear trait will make you misread the dataset, where the readout shows one letter's difference.
- CER:
- Claim, Evidence, Reasoning: make a claim, back it with evidence, explain your reasoning.
- SOP:
- Standard Operating Procedure, the exact steps to follow (especially in a lab).
- Tracker:
- Your PLTW progress log where you record completed evidence.
- myPLTW:
- The PLTW course site where you do the online activities. Find it in Clever with your Microsoft sign-in, right next to Schoology.
Tap the speaker to hear a term. Add two of these to your notebook glossary with a definition and an example in your own words.
Pick just 2 or 3 words from today and make them yours: write what each one means in your own words, name the context clue or evidence that helped, then give one example from what you actually did in SNP and PTC case. Try your own words first; the glossary is there if you get stuck. This is voluntary and counts as extra credit, so keep it short.
Saved on this device. Show Mr. Mendoza or add these to your notebook glossary to claim the extra credit.
Part 2 of 4 · Directions in plain English▸
2.1 Open your materials
Use the materials named in the first step below. Open lesson resources.
2.2 Start the work
Open the teacher genotype dataset (Activity 2.1.3 in myPLTW if it opens) and find the SNP column for the PTC-tasting gene. If myPLTW will not open, use this practice readout at the one assayed position (C marks the PAV, taster, haplotype and G marks AVI): Person 1 CC, tastes PTC; Person 2 CG, tastes PTC; Person 3 GG, does not taste it.
Show all 5 required steps
- Open the teacher genotype dataset (Activity 2.1.3 in myPLTW if it opens) and find the SNP column for the PTC-tasting gene. If myPLTW will not open, use this practice readout at the one assayed position (C marks the PAV, taster, haplotype and G marks AVI): Person 1 CC, tastes PTC; Person 2 CG, tastes PTC; Person 3 GG, does not taste it.
- For three people, write their genotype next to their phenotype and mark homozygous or heterozygous.
- Decide whether the tasting allele tracks with the trait and write one sentence of evidence.
- Predict the carrier status of one labeled person using allele language.
- Submit your genotype-to-phenotype table and prediction as your daily evidence.
Lost your place? If you have not located the SNP column for the PTC gene in the dataset yet, do that first (step 1). If you already have three people's genotype-to-phenotype rows, move to predicting one person's carrier status in allele language (step 4), then submit.
- 0-8Hook: PTC tasting demo or description; introduce vocabulary
- 8-25Open dataset; locate column; record and phenotype for three individuals
- 25-40Mark each as homozygous or heterozygous; decide if tasting tracks phenotype
- 40-55Write one evidence sentence; predict status for one labeled person
- 55-70Partner check: verify language and logic
- 70-80Submit table and prediction as one PDF in Schoology
- • Hook: If PTC strips are available, each student who chooses to taste gets one strip, used once, in a non-lab area away from the benches; otherwise describe the tasting phenotype. Ask who tasted bitterness.
- • Why it matters: This same -to-phenotype logic underlies pharmacogenomics, where a small number of base differences can change how a patient responds to a drug.
- • Today's work: You read a real dataset and connect alleles to phenotypes the same way a lab does.
- • Exit goal: -to-phenotype table and prediction submitted before the bell.
PLTW connection and today's work
Open Activity 2.1.3 Test Your Own Genes in myPLTW and use the teacher genotype dataset to connect SNP alleles to phenotypes.
Today's stopping point: Pedigree should be done; SNP table and carrier prediction due today.
PLTW activity titles identify the course connection. If your account will not open, use the posted materials for today and tell Mr. Mendoza. Do not mark an online activity complete unless you completed it.
Course connection
- Activity 2.1.3 Test Your Own Genes
Use the turn-in directions in Part 4 of this page. Do not create a second submission unless your teacher asks for one.
Show another explanation or a smaller first step
Need help? Choose a starting point
Part 3 of 4 · Worked example▸
This is a parallel case, not your own. Read it for the order of the work, then do your own in Part 4.
Parallel case, not your readout: I used a different single-letter difference, the lactase SNP that sits just before the LCT gene. At the one tested position, T goes with keeping the ability to digest milk sugar as an adult, and C goes with losing it. The three samples below are practice samples for this worked example only.
Does the allele track with the trait? Yes, in these three samples. Samples with at least one T kept the ability to digest milk sugar, and the only sample that lost it was CC. Evidence: Sample A (TT) and Sample B (CT) both digest milk sugar as adults; Sample C (CC) does not, so T tracks with the trait and behaves as dominant here.
Carrier prediction: Sample B is heterozygous (CT). B shows the dominant trait but carries one C allele, so B could pass the C allele to a child.
Your own table uses your readout and your letters, so your genotypes and your carrier call come from your data, not from this example.
| Sample | Genotype | Zygosity | Digests milk sugar as an adult |
|---|---|---|---|
| A | TT | homozygous | yes |
| B | CT | heterozygous | yes |
| C | CC | homozygous | no |
This model shows the level of evidence and organization needed to complete: Completes the SNP case analysis: a genotype-to-phenotype table for three individuals with homozygous or heterozygous labels, an evidence sentence, and a carrier prediction.
- Name the variables and include units.
- Enter observations without changing the raw values.
- Check labels, calculations, and patterns before interpreting the data.
Keep the structure. Replace the question, facts, measurements, and evidence. Then recheck units, vocabulary, and whether the conclusion goes beyond the evidence.
Also due today: Submit your genotype-to-phenotype table and prediction as one PDF to Schoology assignment Wk9 Data table: SNP and PTC case.
A library keeps a master plan protected while working copies guide production at different stations.
- Why protect the master copy?
- What information moves?
- Where can an error change the final product?
Stored information can be copied, read, and converted into a functional product.
Genes are regulated biological sequences, not conscious instructions, and one gene rarely determines a whole trait alone.
- • Master plan maps to .
- • Working copy maps to RNA.
- • Production output maps to or a regulated cell function.
Part 4 of 4 · Your work▸
Check your work before submitting
- You'll be able to read a SNP genotype and pair it to a phenotype.
- You'll be able to predict carrier status from genotype data.
Working rules for today
- Tasting a PTC strip is optional. Skip it if you have a food allergy or any health concern, and use the practice readout on this page instead.
- One strip per student, used once. Never share, reuse, or trade a strip.
- Taste only in a non-lab area, away from the lab benches, with clean hands. Nothing from a lab bench goes in your mouth.
- Put your used strip in the trash right away.
4.1 Turn in your work
DueCheck the Schoology assignment for this day- Hand in
- Genotype-to-phenotype table for three individuals (homozygous/heterozygous labeled) and a written carrier prediction.
How to submit and name your file
Submit as one PDF in Schoology.
In Schoology, open your course and the assignment for this lesson. Attach your file, select Submit, and check that it appears in the submission.
PDF upload helpYou get two school days for every day you were absent, so this deadline moves with you.
Today's lesson is in Schoology
Each school day has one lesson page in Schoology that holds everything for the day: the goal, the story so far, every table and data value, the numbered steps, and what to turn in. Open it first and work from it. The other rows for this day, if any, are the score line for a paper quiz or test and the John Carroll debate item; they do not add work. Check Schoology for each deadline.
- Today's Lesson · Mon 10/19 · Wk9 · How vaccines work, then build a recombinant plasmid for a hepatitis B vaccine(today's lesson page: the goal, the data, the steps, and what to turn in are all on it)
Link will not open? Open Schoology, choose your course and section, and find the title shown above.
- CompleteEvery required part of the artifact is present, nothing left blank.
- AccurateThe science and the data are correct and match the evidence.
- Scientific reasoningYou explain your claim with evidence and reasoning (CER), not just an answer.
- Professional communicationClear, organized, labeled, and written the way a clinician or scientist would.
- SubmittedGo to Schoology to turn this in. Submit one PDF. Schoology attaches your name to your upload; on the page itself, write your period and code. Name the file: FirstName LastName - Assignment Title - YYYY-MM-DD.pdf. If you cannot get in, see Mr. Mendoza. Do not skip the work.
How this lesson connects
Keep using what you learned last class: A pedigree is read by testing each inheritance pattern against every parent and child and keeping only the pattern that fits them all; a carrier is someone the pattern forces to hold a hidden allele even though they show no trait. Today: Three single-base differences in TAS2R38 are inherited together and change the shape of the bitter-taste receptor, so that haplotype is what decides whether PTC tastes bitter or like nothing at all.
Practice: try a question, then check your answer▸
Claim ceiling for this check: Today's evidence supports a classroom claim about today's lesson. It cannot prove causation, diagnose a real patient, or justify action outside this room.
A person's TAS2R38 genotype is heterozygous (one taster allele, one non-taster allele). Will they taste PTC, and are they a carrier of the non-taster allele?
Write an answer and pick a confidence to unlock the key.
Fast retrieval with instant answers, not the commit-then-reveal check above. Try each from memory first: write what you remember about the earlier units, then check yourself here.
Missed class or ready for more?▸
Optional practice for this unit's lab skills. Nothing in it is due today.
What today's skills lead to. These are real health-science careers this course builds toward. Tap one to see, on the US Department of Labor's O*NET site, what the job actually involves, what it pays, and how fast it is growing.
From home, use the practice readout on this page to complete the same case: build the -to-phenotype table for three people and predict one person's status with a written explanation.
Learn.Genetics: SNPs (background; the practice readout is on this page)Submit as one PDF in Schoology.
Class still runs. Complete today's work as this page describes (it is self-guided). Need the concept taught without a teacher? Use this authoritative explainer:
MedlinePlus: What is genetic testing?Sources: slides, readings, and resources▸
The deck carries the prior idea forward, lets you inspect an analogy, maps the rule to biology, and ends with the same evidence decision and exit ticket used on this page.
Play the cold open at the start of the unit to set the scene. Each recording is AI-generated and simulated (fictional callers, no real people or student data).
Classroom documents for this lesson are posted in Schoology. Open Clever, then Schoology, and find each one by the name shown on its card.
Use this after the required lesson work when you are ready for a harder application or a deeper connection.
Use this as the classroom resource for Genetic testing, PTC, pedigree, SNPs.
Use this if you were absent, got stuck, or need another pass before you submit the lesson artifact.
Sign in to Clever with your district Microsoft account to open Schoology or myPLTW. Follow today's posted steps. If myPLTW will not open, use the posted alternative and tell Mr. Mendoza. Turn in your completed work through the Schoology assignment.
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