Week 12 — Quiz (auto-graded) · Patterns of Inheritance

Course: Introduction to Biology — General Biology I (BIOL 101) · Silver Oak University (fictional sample) · Prof. Castellano
Objective tested: Objective 6 — incomplete dominance vs. codominance; multiple alleles & the ABO blood-type system; sex linkage (X-linked recessive) & carriers; reading human pedigrees.
Points: 10 (1 each) · Assignment group: Quizzes (10% of grade) · Due: end of Module 12.

This is the human-readable quiz with its vetted answer key and feedback. The import-ready Classic QTI is in F-quiz-week-12-qti.xml (generated by the shared validated script — parses with 10 items, every single-answer item exactly one correct). The reusable item-bank entries and the Canvas placement block are at the bottom of this file. Every numeric answer is pre-computed and independently re-verified (see the Quality gate).

Blueprint

No trick questions; distractors target the Week 12 misconceptions named in the lecture outline. All probabilities are engineered to clean values and re-derived in a Python check.

Questions, key, and feedback

Q1 (MC). A true-breeding red snapdragon (RR) is crossed with a true-breeding white one (WW), and all the F₁ offspring are pink. The heterozygote shows a new, in-between phenotype. This pattern is —
- A. codominance
- B. incomplete dominance ✅
- C. complete dominance
- D. a sex-linked trait
Feedback: Incomplete dominance — the heterozygote is a blend (red + white = pink), an in-between look. (Codominance would show both colors at once, not a blend; complete dominance would make the heterozygote look fully red.)

Q2 (MC). A person with type AB blood produces both the A antigen and the B antigen at the same time — not a blend. The relationship between the Iᴬ and Iᴮ alleles is —
- A. incomplete dominance
- B. codominance ✅
- C. recessive inheritance
- D. complete dominance
Feedback: Codominance — both alleles are fully expressed side by side (A and B antigens). The tell vs. incomplete dominance: codominance shows both originals at once; incomplete dominance makes a new in-between (like pink).

Q3 (MC). Two pink snapdragons are crossed (RW × RW, where RW = pink). What fraction of the offspring are expected to be pink?
- A. 1/4
- B. 1/2 ✅
- C. 3/4
- D. all of them
Feedback: The 2×2 Punnett square gives genotypes 1 RR : 2 RW : 1 WW, which (with the blend rule) are 1 red : 2 pink : 1 white. Pink is 2 of 4 = 1/2. (The phenotype ratio 1:2:1 matches the genotype ratio because every genotype looks different.)

Q4 (MC). A parent with type A blood (genotype Iᴬi) has children with a parent who has type B blood (genotype Iᴮi). What is the probability that a child has type O blood?
- A. 0
- B. 1/4 ✅
- C. 1/2
- D. 3/4
Feedback: Each parent carries a hidden recessive i. The square gives IᴬIᴮ (AB), Iᴬi (A), Iᴮi (B), ii (O) — each 1/4, so P(type O) = 1/4. Two parents who show A and B can still produce a type-O child.

Q5 (MC). Type O is the most common ABO blood type in many populations. A student concludes, "type O must be dominant." Why is this wrong?
- A. Type O is actually very rare
- B. The i allele is recessive; type O requires two copies (ii) — it's common because i is a frequent allele, not because it's dominant ✅
- C. Blood type is not inherited
- D. Type O blood has both the A and B antigens
Feedback: Frequency is not dominance. The i allele is recessive, so type O needs two copies (ii). O is common because the i allele happens to be frequent in the population — not because it "wins." (Type O has no A or B antigen, which is why O is the universal red-cell donor.)

Q6 (Multiple answer — select all that apply). Which of the following statements about an X-linked recessive trait (such as red-green colorblindness) are true?
- A. A male (XY) has only one X, so a single recessive allele makes him affected ✅
- B. A male can be an unaffected "carrier" of the trait
- C. A female can be an unaffected carrier if she has one recessive and one normal allele (XᴬXᵃ) ✅
- D. The trait is more common in males than in females ✅
- E. The allele for the trait is carried on the Y chromosome
Feedback: A male is hemizygous (one X), so one recessive allele = affected (A), and there is no male carrier (B is false). A female with XᴬXᵃ is an unaffected carrier (C), and the trait is more common in males (D) because they have no back-up X. The allele is on the X, not the Y (E is false).

Q7 (MC). A carrier mother (XᴬXᵃ) for red-green colorblindness has children with an unaffected father (XᴬY). What fraction of their sons are expected to be colorblind?
- A. 0
- B. 1/2 ✅
- C. 1/4
- D. all of them
Feedback: Mom's gametes are Xᴬ or Xᵃ; sons receive a Y from dad, so a son is XᴬY (normal) or XᵃY (colorblind) — 1/2 of sons are affected. (Daughters all get dad's Xᴬ, so 1/2 are carriers and 0 are affected; across all children, 1/4 are affected, and they're all male.)

Q8 (True / False). "A man can be an unaffected carrier of red-green colorblindness, passing it to his children while never being colorblind himself."
- True
- False ✅
Feedback: False. A male has only one X, so for an X-linked recessive trait he is affected (XᵃY) or not (XᴬY) — there is no male carrier. Only females (two X's) can carry the allele silently as XᴬXᵃ. (A son also receives his single X from his mother, not his father.)

Q9 (MC). In a pedigree, individual I-1 (an unaffected father) and I-2 (an unaffected mother) have a son, II-1, who is affected by a trait. What does this most directly tell you?
- A. The trait must be dominant
- B. The trait must be recessive (each unaffected parent carried a hidden copy) ✅
- C. The trait must be carried on the Y chromosome
- D. The trait cannot be inherited at all
Feedback: If neither parent shows the trait but a child does, each parent must have carried a hidden (recessive) copy — so the trait is recessive. (Because the only affected individual here is male, this pattern is also consistent with X-linked recessive, with the mother an obligate carrier — but "recessive" is the direct conclusion from two unaffected parents.)

Q10 (Matching). Match each genotype to the ABO blood type it produces.
| Genotype | Correct blood type |
|---|---|
| Iᴬ Iᴬ | Type A |
| Iᴮ i | Type B |
| Iᴬ Iᴮ | Type AB |
| i i | Type O |
Feedback: Iᴬ makes the A antigen and Iᴮ makes the B antigen; i is recessive and makes none. So IᴬIᴬ = A, Iᴮi = B (the i is masked by Iᴮ), IᴬIᴮ = AB (codominant — both antigens), and ii = O (no antigen). (IᴬIᴬ and Iᴬi both give type A; IᴮIᴮ and Iᴮi both give type B.)

Answer key (quick reference)

Quality gate (self-checked): each single-answer item has exactly one correct option; the multiple-answer item (Q6) lists the three true statements (A, C, D) and requires B and E to be left unselected; the matching item (Q10) pairs four genotypes to four distinct blood types; no item asserts a fact outside the Week 12 course definitions. Every probability is pre-computed and independently re-verified by a Python check that re-derives the fractions from first principles: RW × RW → P(pink) = 1/2 (Q3); type A (Iᴬi) × type B (Iᴮi) → P(type O) = 1/4 (Q4); carrier mom (XᴬXᵃ) × unaffected dad (XᴬY) → 1/2 of sons colorblind, 1/4 of all children affected (Q7). The check printed PASS — quantitative gate: PASS. The codominance/incomplete-dominance distinction (Q1, Q2) and the "type O is dominant" trap (Q5) are vetted against the lecture definitions.

Item-bank entries (for variants + the midterm/final)

All ten items are tagged course=BIOL101 · week=12 · objective=6 · topic=patterns-of-inheritance and deposited in Item Bank: Week 12 — Patterns of Inheritance. The final (Week 16) and the per-term variant updates draw fresh items from this bank. (Tags: q1 incomplete-dominance, q2 codominance, q3 incomplete-cross-half-pink, q4 abo-cross-quarter-O, q5 type-O-not-dominant, q6 sex-linkage-true, q7 sex-linkage-half-sons, q8 no-male-carrier, q9 pedigree-recessive, q10 abo-genotype-match.)

Canvas placement block

canvas_object   = Quizzes::Quiz
title           = "Week 12 Quiz — Patterns of Inheritance"
assignment_group = "Quizzes"
points_possible = 10
grading_type    = points
due_offset_days = 5        # 5 days after module start (Sun of the module week)
published       = true
shuffle_answers = true
provenance      = "~ Prof. Castellano's edition · Fall 2026 · built with thecoursemaker.com"