Week 12 — Lab / Scientific Inquiry · "Blood-Type & Pedigree Detective"

Course: Introduction to Biology — General Biology I (BIOL 101) · Silver Oak University (fictional sample) · Prof. Castellano
Objective: Objective 6 — use Punnett squares and probability for non-Mendelian patterns (ABO multiple alleles, sex linkage) and read a pedigree · SLO A (quantitative scientific reasoning; data interpretation)
Worth 50 points · Labs group = 15% of the grade · Lab 12
Format: a virtual / paper problem set — you'll work blood-type and sex-linkage crosses, complete a probability data table, read a pedigree, and then catch the AI's mistakes when it interprets the cases.

This is the course's signature weekly component. Every instructional week has one lab. This week's lab is a "dry lab" — a genetics problem set built on a free, verified online reference instead of a wet bench. All lab resources are links to external sites — nothing to buy or download.

---

Part 1 — The Big Picture

This week you learned that real inheritance extends past Mendel: alleles can blend (incomplete dominance) or be co-expressed (codominance, like AB blood), a gene can have multiple alleles (the ABO system), and a gene can ride on the X chromosome (sex linkage). Today you become the genetic-cross detective: given parents' genotypes, you'll predict offspring probabilities exactly, and given a family pedigree, you'll deduce how a trait is inherited — the same reasoning a genetic counselor uses.

The "phenomenon": from just two parents' genotypes, the laws of probability let you predict the odds for each possible child — and a family tree (pedigree) lets you run that logic backward to figure out whether a trait is dominant or recessive, autosomal or X-linked.

Background references (open these first — each verified live):
- Learn.Genetics (Utah) — "Genes and Blood Type" (how the Iᴬ, Iᴮ, i alleles make the A/B/AB/O types): 🔗 https://learn.genetics.utah.edu/content/basics/blood/
- Learn.Genetics (Utah) — "Sex Linkage" (why X-linked traits are more common in males): 🔗 https://learn.genetics.utah.edu/content/pigeons/sexlinkage/
- Amoeba Sisters — "Pedigrees" (how to read the symbols): 🔗 https://www.youtube.com/watch?v=Gd09V2AkZv4

---

Part 2 — Your Scientific Question & Hypothesis

The question: Given two parents' genotypes, can you predict the probability of each offspring outcome — and can you read a pedigree backward to determine how a trait is inherited?

Before you start, write a hypothesis about ONE of the cases below (an "if… then…" statement is perfect):

If a type-A parent (Iᴬi) and a type-B parent (Iᴮi) have children, then I predict the chance of a type-O child is __, because ____.

Write it down now — you'll compare it to the worked probabilities at the end. (A "wrong" prediction is completely fine; the point is to test it against the Punnett square.)

---

Part 3 — Materials & Procedure

You need (all free):
- A browser to open the verified Learn.Genetics references above (and the Amoeba Sisters pedigree video).
- Paper or a blank doc to draw Punnett squares (a 2×2 grid for each cross).
- An approved chatbot (Gemini, Claude, or ChatGPT) for Part 7 — but do the crosses yourself first.

Procedure — work the three cases in order, drawing each Punnett square:

1. Case A — Incomplete dominance (snapdragons). Cross RW × RW (R = red, W = white; RW = pink). Put R and W on the edges, fill the four boxes, label each genotype's phenotype (RR = red, RW = pink, WW = white), and record the fraction pink.
2. Case B — ABO multiple alleles. Cross type A (Iᴬi) × type B (Iᴮi). List each parent's gametes, fill the square, label each box's blood type, and record the fraction of each type (A, B, AB, O).
3. Case C — Sex linkage. Cross a carrier mother (XᴬXᵃ) × unaffected father (XᴬY) for red-green colorblindness. List the gametes (mother: Xᴬ/Xᵃ; father: Xᴬ/Y), fill the square, label each box (son/daughter; normal/carrier/colorblind), and record the fraction of sons colorblind and the fraction of daughters colorblind.
4. Case D — Pedigree. Read the pedigree described in Part 6 and decide how the trait is inherited.

Prefer a guided interactive? The Learn.Genetics blood-type page walks the ABO genotype→type logic, and the Amoeba Sisters "Pedigrees" video walks a worked family. Use them to check your reasoning — but fill the squares yourself; that's the graded skill.

---

Part 4 — Data Table (fill this in)

Record the probability you get from each Punnett square. (Express as a fraction and a percent.)

Cross	Outcome asked	Your predicted probability
A. RW × RW (incomplete dominance)	P(pink offspring)	______
B. Iᴬi × Iᴮi (ABO)	P(type O child)	______
B. Iᴬi × Iᴮi (ABO)	P(type AB child)	______
C. XᴬXᵃ × XᴬY (sex linkage)	Fraction of sons colorblind	______
C. XᴬXᵃ × XᴬY (sex linkage)	Fraction of daughters colorblind	______
C. XᴬXᵃ × XᴬY (sex linkage)	Fraction of all children affected	______

Show each Punnett square next to its row, or attach your sketches.

---

Part 5 — Identify Your Experiment's Parts

Answer in a sentence each (yes — even a "dry lab" has a structure to name):
1. Independent variable (what differs from cross to cross): __
2. Dependent variable (what you predict/measure): _
3. A controlled assumption (something held the same across all crosses — e.g., the offspring sex ratio, random fertilization):
4. The "model" you used to make the predictions: ___

---

Part 6 — Analysis Questions

Read this pedigree (described in words): GENERATION I — an unaffected father (I-1, unshaded square) and an unaffected mother (I-2, unshaded circle). GENERATION II (their children) — an affected son (II-1, shaded square) and two unaffected daughters (II-2 and II-3, unshaded circles).

1. Case A: what is the chance of a pink offspring from RW × RW, and why does the phenotype ratio (1:2:1) match the genotype ratio here but not in a normal dominant/recessive cross?
2. Case B: two parents show blood types A and B, yet one of their children can be type O. Explain how, using the idea of a hidden recessive allele (i). What is P(type O)?
3. Case C: explain why 1/2 of the sons but 0 of the daughters are colorblind in this cross. Why can a daughter be an unaffected carrier but a son cannot?
4. Pedigree (Case D): Is the trait dominant or recessive? Autosomal or X-linked? Give the reasoning (use the two decision rules from class). What is mother I-2's genotype if it's X-linked recessive, and the chance a future son is affected?
5. Connect it: which idea from this week (incomplete dominance, codominance, multiple alleles, or sex linkage) most surprised you, and how does the Punnett-square method let you predict odds even when Mendel's simple dominant/recessive rule doesn't apply?

---

Part 7 — AI-Critique Moment (required — this is the BYOAI step)

Now bring in your approved chatbot (Gemini, Claude, or ChatGPT) and be the scientist who checks its work.

1. Paste Case C and the pedigree to the chatbot and ask: "For a carrier mother (XᴬXᵃ) and an unaffected father (XᴬY), what fraction of sons and daughters are colorblind, and can a son be a carrier? Then, for a pedigree where two unaffected parents have an affected son and two unaffected daughters, is the trait dominant or recessive, and autosomal or X-linked?"
2. Check everything it says against your own Punnett squares and pedigree logic:
   - Did it get 1/2 of sons and 0 of daughters colorblind — or did it swap the son/daughter fractions?
   - Did it correctly say a son cannot be a carrier (one X → affected or not) — or did it wrongly call a son a "carrier"? (Chatbots do this constantly.)
   - On the pedigree, did it conclude recessive (two unaffected parents → affected child) — or did it call it dominant?
   - Watch for the deeper slip: does it ever confuse incomplete dominance with codominance if you ask about Case A? (Pink = blend = incomplete; AB = both = codominant.)
3. Write 2–3 sentences reporting what the AI got right and at least one thing you had to correct or watch carefully. (If it happened to get everything right, say how you verified each claim against your own square — that's the skill.)

The habit all term: the tool drafts, you judge. A chatbot will confidently flip your sex-linkage fractions or invent a "male carrier" — catching it is the point.

---

Part 8 — What to Submit

Submit a single document (or text entry) with: your hypothesis, your completed probability data table with your Punnett-square sketches, your Part 5 structure labels, your Part 6 answers (including the pedigree conclusion), and your Part 7 AI-critique paragraph. Due Sunday, Nov 22, 11:59 p.m. (50 points).

---

Instructor answer key & model data — REMOVE BEFORE PUBLISHING TO STUDENTS

Every probability below is pre-computed and independently re-verified by a Python check that re-derives each fraction from first principles (RW × RW → 1/2 pink; Iᴬi × Iᴮi → AB/A/B/O each 1/4; XᴬXᵃ × XᴬY → 1/2 of sons, 0 of daughters, 1/4 of all children affected). The check printed PASS.

Model probability table (the correct answers):

Cross	Outcome	Correct probability
A. RW × RW	P(pink)	2/4 = 1/2 = 50%
B. Iᴬi × Iᴮi	P(type O)	1/4 = 25%
B. Iᴬi × Iᴮi	P(type AB)	1/4 = 25% (and 1/4 A, 1/4 B)
C. XᴬXᵃ × XᴬY	sons colorblind	1/2 of sons
C. XᴬXᵃ × XᴬY	daughters colorblind	0 of daughters (1/2 are carriers)
C. XᴬXᵃ × XᴬY	all children affected	1/4 (all male)

Worked squares (for grading):
- Case A (RW × RW): boxes RR, RW, RW, WW → 1 red : 2 pink : 1 white → P(pink) = 2/4 = 1/2. The phenotype ratio matches the genotype ratio (1:2:1) because each genotype has a distinct look (no masking).
- Case B (Iᴬi × Iᴮi): gametes Iᴬ/i and Iᴮ/i → boxes IᴬIᴮ (AB), Iᴬi (A), Iᴮi (B), ii (O) → each 1/4. P(type O) = 1/4; P(type AB) = 1/4. Each parent carried a hidden i.
- Case C (XᴬXᵃ × XᴬY): mother's gametes Xᴬ/Xᵃ, father's gametes Xᴬ/Y → boxes XᴬXᴬ (daughter, normal), XᴬY (son, normal), XᴬXᵃ (daughter, carrier), XᵃY (son, colorblind). Sons: 1/2 colorblind. Daughters: 0 colorblind, 1/2 carriers. All children: 1/4 affected, all male.

Expected answers:
- Part 5: (1) IV = the parents' genotypes / the type of cross; (2) DV = the predicted probability of an offspring outcome; (3) controlled assumption = random fertilization and an even ~50:50 chance of son vs. daughter (each child independent); (4) the model = the Punnett square + the laws of probability (product rule).
- Part 6: (1) P(pink) = 1/2; the 1:2:1 phenotype ratio matches the genotype ratio because in incomplete dominance every genotype (RR, RW, WW) looks different — nothing is masked. (2) P(type O) = 1/4; each A/B parent carries a hidden recessive i, and a child who inherits i from both parents is ii = type O. (3) Sons get a Y from dad and their only X from mom, so a son with the mother's Xᵃ is colorblind → 1/2 of sons; daughters all get dad's Xᴬ, so none can be XᵃXᵃ → 0 affected, but those who get mom's Xᵃ are carriers (XᴬXᵃ) → 1/2 carriers. A daughter has two X's (one can mask the recessive allele → carrier); a son has one X (nothing to mask it → affected or not). (4) Recessive (two unaffected parents → affected child); X-linked recessive is well supported (only affected individual is male; mother is the carrier) — autosomal recessive is formally possible from this small pedigree, but the male-skew is the deciding clue; mother I-2 is an obligate carrier (XᴬXᵃ); a future son has a 1/2 chance of being affected. (5) Any thoughtful answer; full credit for noting that the Punnett square + probability works for any pattern once you know how each genotype maps to a phenotype.
- Part 7 (AI-critique): full credit for a specific catch — most commonly the AI swapping the son/daughter fractions, inventing a "male carrier," calling the pedigree dominant, or confusing incomplete dominance with codominance. Full credit also if the student verified each AI claim against their own squares and pedigree logic.

Grading rubric — 50 points

Criterion	Full	Partial	None
Hypothesis — a clear, testable "if…then…" prediction with a reason (8)	8	4–6	0–2
Data table + Punnett squares — all six probabilities correct with squares shown (15)	15	8–12	0–6
Structure (Part 5) — IV, DV, a controlled assumption, and the model all named (12)	12	6–10	0–4
Analysis (Part 6) — correct cross reasoning + correct pedigree conclusion (recessive, X-linked, mother carrier, future son 1/2) (10)	10	5–8	0–4
AI-critique (Part 7) — names a specific thing checked/corrected in the AI's interpretation (5)	5	3	0–2

Quality gate (self-checked): every probability in the model table is pre-computed and independently re-verified by a Python re-derivation that printed PASS — quantitative gate: PASS (RW × RW → 1/2 pink; Iᴬi × Iᴮi → AB/A/B/O each 1/4, so P(O) = 1/4 and P(AB) = 1/4; XᴬXᵃ × XᴬY → 1/2 of sons colorblind, 0 of daughters affected, 1/4 of all children affected). The biology is correct (incomplete dominance = blend; codominance = both; i is recessive; males are hemizygous with no carrier state; pedigree logic of two-unaffected-parents-→-recessive). The pedigree is fully described in text so the analysis is gradable without a figure, and no student-collected number is asserted as "the" answer — the key grades the reasoning and the squares.