Week 11 — Quiz (auto-graded) · Mendelian Genetics

Course: Introduction to Biology — General Biology I (BIOL 101) · Silver Oak University (fictional sample) · Prof. Castellano
Objective tested: Objective 6 — segregation; genotype vs. phenotype; the monohybrid Punnett square; probability (the product rule); the test cross; the dihybrid 9:3:3:1.
Points: 10 (1 each) · Assignment group: Quizzes (10% of grade) · Due: end of Module 11.

This is the human-readable quiz with its vetted answer key and feedback. The import-ready Classic QTI is in F-quiz-week-11-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 item is auto-gradable multiple choice with the pre-computed fractions as options.

Blueprint

No trick questions; distractors target the Week 11 misconceptions named in the lecture outline. Every genetics number is pre-computed and independently re-verified (quantitative gate: PASS).

Questions, key, and feedback

Q1 (MC). A pea plant has the genotype Tt and is tall. The word phenotype refers to —
- A. the two alleles the plant carries (Tt)
- B. the plant's observable trait — being tall ✅
- C. the gamete the plant produces
- D. the chromosome the gene sits on
Feedback: Phenotype is the trait you can observe (tall); the genotype is the alleles behind it (Tt). "Genotype is the recipe; phenotype is the cake."

Q2 (MC). An organism with the genotype Tt (one dominant and one recessive allele) is best described as —
- A. homozygous dominant
- B. homozygous recessive
- C. heterozygous ✅
- D. true-breeding
Feedback: Heterozygous means two different alleles (Tt). Two of the same allele is homozygous — TT (homozygous dominant) or tt (homozygous recessive).

Q3 (Multiple answer — select all that apply). Which of the following statements are true?
- A. An allele is a version of a gene (e.g., T for tall, t for short) ✅
- B. Dominant alleles are always more common in a population than recessive ones
- C. TT and Tt look the same (both tall) but produce different offspring ratios when crossed ✅
- D. By the law of segregation, each parent passes only ONE allele of a gene to each offspring ✅
- E. Genotype and phenotype always mean the same thing
Feedback: A, C, and D are core Week-11 facts. B is false — dominant means "the allele that shows," not "more common" (recessive alleles can be the majority). E is false — TT and Tt share a phenotype but differ in genotype.

Q4 (MC). Two heterozygous tall pea plants are crossed: Tt × Tt. Filling the four boxes gives TT, Tt, Tt, tt. The phenotype ratio (dominant : recessive) is —
- A. 1 : 1
- B. 1 : 2 : 1
- C. 3 : 1 ✅
- D. 9 : 3 : 3 : 1
Feedback: Any plant with at least one T is tall, so 3 of the 4 boxes (TT, Tt, Tt) are tall and 1 (tt) is short → 3 : 1. Careful: 1 : 2 : 1 is the genotype ratio, not the phenotype ratio.

Q5 (MC). In that same Tt × Tt cross, what is the probability that a single offspring shows the recessive (short) trait?
- A. 1/2
- B. 1/4 ✅
- C. 3/4
- D. 1/16
Feedback: The short trait needs a t from each parent: P = 1/2 × 1/2 = 1/4 (the single tt box out of four). P(dominant) is the other 3/4.

Q6 (Matching). Match each cross to the offspring ratio it produces.
| Cross | Correct ratio |
|---|---|
| Tt × Tt (monohybrid, two heterozygotes) | 3 dominant : 1 recessive |
| Tt × tt (test cross) | 1 dominant : 1 recessive |
| TT × tt (homozygous dominant × homozygous recessive) | All dominant (100%) |
| TtYy × TtYy (dihybrid, both heterozygous) | 9 : 3 : 3 : 1 |
Feedback: Tt × Tt → 3:1; the test cross Tt × tt → 1:1; TT × tt → all dominant (every offspring is Tt); the dihybrid TtYy × TtYy → 9:3:3:1 (two independent 3:1 crosses multiplied).

Q7 (MC). A test cross mates a heterozygote with a homozygous recessive: Tt × tt. What is the probability that an offspring shows the dominant trait?
- A. 3/4
- B. 1/4
- C. 1/2 ✅
- D. 1 (all of them)
Feedback: The tt parent can pass only t, so the offspring are half Tt (dominant) and half tt (recessive): boxes Tt, Tt, tt, tt → 1/2 dominant, 1/2 recessive (1:1). (If the unknown parent were TT, every offspring would be tall — that contrast is what a test cross reveals.)

Q8 (True / False). "A 3:1 phenotype ratio from a Tt × Tt cross guarantees that a family of exactly four offspring will have exactly 3 dominant and 1 recessive."
- True
- False ✅
Feedback: False. 3:1 is a probability (3/4 dominant, 1/4 recessive) — the long-run expectation over many offspring, like coin flips. A family of four could be all tall, or 2-and-2. The ratio is reliable across large numbers, not guaranteed in four.

Q9 (MC). In a dihybrid cross TtYy × TtYy (T = tall/short, Y = yellow/green), what is the probability of an offspring recessive for both traits (ttyy)?
- A. 1/4
- B. 9/16
- C. 1/16 ✅
- D. 3/16
Feedback: Each trait alone is a 3:1 cross, so P(short) = 1/4 and P(green) = 1/4. By the product rule, P(both recessive) = 1/4 × 1/4 = 1/16 — the smallest class in the 9:3:3:1 ratio. (P(both dominant) = 3/4 × 3/4 = 9/16.)

Q10 (MC). A student says, "The tall allele is dominant, so most pea plants in the world must be tall, and the tall allele must be 'stronger.'" The best correction is —
- A. Correct — dominant alleles are always more common and stronger
- B. Dominant means the allele's trait shows when present; it says nothing about how common the allele is or how 'strong' it is ✅
- C. Dominant alleles are rarer than recessive ones in every population
- D. There is no difference between dominant and recessive alleles
Feedback: Dominance is about masking, not frequency or strength. A dominant trait can be rare and a recessive trait common (most people in Scandinavia carry the recessive light-eye alleles). Allele frequency depends on the population's history, not on which allele is dominant.

Answer key (quick reference)

Quality gate (self-checked): each single-answer item has exactly one correct option; the multiple-answer item lists all three true statements (A, C, D) and requires B and E to be left unselected; the matching item pairs four crosses to four distinct ratios; no item asserts a fact outside the Week 11 course definitions. Every genetics number was re-derived by an independent Python check that re-computes the monohybrid 1:2:1 and 3:1, the dihybrid 9:3:3:1, and the probabilities 1/4, 3/4, 1/2, 1/16, 9/16 and the coin-toss 75:25 — all match the pre-computed values (quantitative gate: PASS). Numeric items (Q5, Q7, Q9) are auto-gradable multiple choice with the computed fractions as the options.

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

All ten items are tagged course=BIOL101 · week=11 · objective=6 · topic=mendelian-genetics and deposited in Item Bank: Week 11 — Mendelian Genetics. The final (Week 16) and the per-term variant updates draw fresh items from this bank. (Tags: q1 genotype-phenotype, q2 homo-hetero, q3 alleles-dominance-segregation, q4 monohybrid-phenotype-ratio, q5 p-recessive-quarter, q6 cross-to-ratio-match, q7 test-cross-half, q8 ratio-not-guaranteed, q9 dihybrid-both-recessive, q10 dominant-not-common.)

Canvas placement block

canvas_object   = Quizzes::Quiz
title           = "Week 11 Quiz — Mendelian Genetics"
assignment_group = "Quizzes"
points_possible = 10
grading_type    = points
due_offset_days = 5        # 5 days after module start (Sun Nov 15)
published       = true
shuffle_answers = true
provenance      = "~ Prof. Castellano's edition · Fall 2026 · built with thecoursemaker.com"