{ "format": "recallweave-deck/1", "title": "Inheritance: from gametes to probabilities", "attribution": "Original RecallWeave lesson, scenarios and explanations (2026). Hypothetical diploid plant crosses: autosomal loci, normal equal segregation, random fertilization and no mutation. Complete dominance and independent assortment apply only where stated; the lab also assumes no interaction between the two trait mappings. Probabilities describe zygotes, not guaranteed finite offspring counts or survival. R1: OpenStax Biology 2e §12.3, https://openstax.org/books/biology-2e/pages/12-3-laws-of-inheritance ; R2: §12.2, https://openstax.org/books/biology-2e/pages/12-2-characteristics-and-traits ; R3: NHGRI Meiosis, https://www.genome.gov/genetics-glossary/Meiosis ; R4: NHGRI Genotype, https://www.genome.gov/genetics-glossary/genotype ; R5: NHGRI Phenotype, https://www.genome.gov/genetics-glossary/Phenotype . Sources checked 2026-10-08. Companion guide contains worked transfers and scope limits.", "license": "Original course text and questions: CC0-1.0. Reference sources retain their own terms. No source passages, figures or exercises are reproduced.", "concepts": [ "Alleles and segregation", "Genotype and phenotype", "One-locus crosses", "Independent two-locus crosses" ], "items": [ { "id": "mi-segregation-1", "concept": "Alleles and segregation", "prerequisites": [], "prompt": "A hypothetical diploid plant has genotype Aa at one autosomal locus. With normal segregation and no mutation, which allele content can a gamete carry at this locus?", "options": [ "One allele: either A or a", "Both A and a together", "Only A, because A is dominant", "Neither allele, because the gamete is haploid" ], "answer": 0, "explanation": "A gamete has one allele at this locus. The two alternatives are A and a; haploid does not mean that the locus disappears. Dominance does not decide which allele enters a gamete. [R1, R3]", "transfer": "Replace Aa with AA. What changes about the possible gamete alleles, and what stays the same about the number of alleles per gamete?" }, { "id": "mi-segregation-2", "concept": "Alleles and segregation", "prerequisites": [], "prompt": "Assume equal segregation in an Aa plant. What is the probability that a randomly chosen gamete carries a?", "options": [ "0", "1/4", "1/2", "1" ], "answer": 2, "explanation": "The two allele alternatives have equal probability, so P(a) = 1/2. This describes the model for a random gamete; it does not require every small collected sample to contain equal counts. [R1]", "transfer": "If a source pool contains only gametes from an aa plant, what is P(a)? Explain why the plant's two a copies do not give a gamete two alleles." }, { "id": "mi-segregation-3", "concept": "Alleles and segregation", "prerequisites": [], "prompt": "A learner claims: “Because A is dominant, an a allele in an Aa plant turns into A when gametes form.” Which correction fits the model?", "options": [ "Dominance makes only the a allele enter gametes.", "Dominance describes the Aa phenotype; either allele can be transmitted without changing into the other.", "The two alleles blend into an intermediate allele in every gamete.", "Both alleles must remain together so the dominant one can act." ], "answer": 1, "explanation": "The claim confuses expression with transmission. Under this model, an Aa plant transmits A or a; the allele symbol is not rewritten by dominance. A dominant phenotype in the parent therefore does not imply A-only gametes. [R1, R2]", "transfer": "How could an Aa plant show the dominant phenotype yet contribute a to an aa offspring? Name the contribution needed from the other parent." }, { "id": "mi-phenotype-1", "concept": "Genotype and phenotype", "prerequisites": [ "Alleles and segregation" ], "prompt": "In a hypothetical plant trait with complete dominance of A over a, which genotypes share the A-dominant phenotype?", "options": [ "AA and aa", "Aa and aa", "All three genotypes must have different phenotypes", "AA and Aa" ], "answer": 3, "explanation": "Complete dominance maps both AA and Aa to the A-dominant phenotype; aa maps to the recessive phenotype. These are still three distinct genotypes. The explorer uses this specified mapping, not a rule that applies to every trait. [R2, R4, R5]", "transfer": "Could two plants with the same phenotype produce different gamete types at this locus? Give their possible genotypes." }, { "id": "mi-phenotype-2", "concept": "Genotype and phenotype", "prerequisites": [ "Alleles and segregation" ], "prompt": "A plant has the A-dominant phenotype under complete dominance. No parental or offspring information is available. Which genotype conclusion is justified?", "options": [ "It must be AA.", "It could be AA or Aa.", "It must be Aa.", "It must be aa." ], "answer": 1, "explanation": "The observed phenotype is compatible with both AA and Aa. One observation cannot distinguish two genotypes that this model maps to the same phenotype. Recessive aa would instead have the recessive phenotype. [R2, R4, R5]", "transfer": "Propose a cross partner that could reveal whether this plant can transmit a. What observation would be decisive, and what observation would leave uncertainty?" }, { "id": "mi-phenotype-3", "concept": "Genotype and phenotype", "prerequisites": [ "Alleles and segregation" ], "prompt": "Consider a different trait in which AA, Aa and aa have three distinguishable phenotypes. Equal segregation and random fertilization still hold. An Aa × Aa cross has genotype probabilities 1/4 AA, 1/2 Aa and 1/4 aa. What follows?", "options": [ "The genotype probabilities can stay the same while the phenotypes form three categories with probabilities 1/4, 1/2 and 1/4.", "Equal segregation must fail because Aa looks different.", "All offspring must now have genotype Aa.", "The phenotype probabilities must still be 3/4 dominant and 1/4 recessive." ], "answer": 0, "explanation": "The stated genotype distribution already follows from the gamete combinations. A different genotype-to-phenotype mapping does not by itself change those combinations. Here all three genotypes are distinguishable, so their probabilities give three phenotype categories. The lab's complete-dominance phenotype display does not represent this trait. [R2]", "transfer": "Which part of a cross calculation would you replace for this new trait: the gamete combinations, the phenotype mapping, or both? State what additional evidence could require changing the gamete model too." }, { "id": "mi-cross-1", "concept": "One-locus crosses", "prerequisites": [ "Alleles and segregation", "Genotype and phenotype" ], "prompt": "Under equal segregation and random fertilization, what is P(Aa) for an Aa × Aa cross?", "options": [ "1/4", "3/4", "1/2", "1" ], "answer": 2, "explanation": "A from parent 1 with a from parent 2 gives Aa, and a from parent 1 with A from parent 2 also gives Aa. Each route has probability 1/4, so P(Aa) = 1/4 + 1/4 = 1/2. Genotype Aa has two routes even though it is written only once in the summary.", "transfer": "In the lab, select each route to Aa. Then explain why listing the three genotype names AA, Aa and aa does not make them equally probable." }, { "id": "mi-cross-2", "concept": "One-locus crosses", "prerequisites": [ "Alleles and segregation", "Genotype and phenotype" ], "prompt": "A plant known to be either AA or Aa is crossed with aa. At least one offspring is aa. Assume the stated parents are correct, inheritance follows this model and there is no mutation. What must the unknown parent be?", "options": [ "AA, because its phenotype was dominant.", "Either AA or Aa; an AA parent can supply a.", "aa, because an offspring is aa.", "Aa, because it supplied a and AA cannot do so." ], "answer": 3, "explanation": "The aa partner supplies a. An aa offspring also needs a from the unknown parent. That parent cannot be AA under the assumptions, so the allowed alternative is Aa. This uses an impossible-versus-possible distinction; it does not require guessing a prior probability.", "transfer": "If this cross instead produced only A-dominant offspring in a small sample, would that prove the unknown parent is AA? Explain using a possible Aa route." }, { "id": "mi-cross-3", "concept": "One-locus crosses", "prerequisites": [ "Alleles and segregation", "Genotype and phenotype" ], "prompt": "Two independently formed seeds from Aa × Aa are labeled left and right before their phenotypes are known. Assume complete dominance. What is the probability that the left seed has the A-dominant phenotype AND the right seed has the recessive phenotype?", "options": [ "3/4", "1/4", "1/16", "3/16" ], "answer": 3, "explanation": "One seed has P(A-dominant) = 3/4 and P(recessive) = 1/4. The requested ordered outcome uses both independent events: (3/4) × (1/4) = 3/16. The four gamete routes are probabilities for each fertilization, not a quota that every small group of seeds must meet.", "transfer": "What if the question asks for one dominant and one recessive seed in either order? List the two disjoint orders before adding their probabilities." }, { "id": "mi-independent-1", "concept": "Independent two-locus crosses", "prerequisites": [ "One-locus crosses" ], "prompt": "An AaBb plant has two independently assorting autosomal loci with equal segregation. Which gamete distribution follows?", "options": [ "AB and ab only, each with probability 1/2", "AB, Ab, aB and ab, each with probability 1/4", "Aa and Bb only, each with probability 1/2", "AABB, AaBb and aabb, each with probability 1/3" ], "answer": 1, "explanation": "A gamete carries one allele from the A locus and one from the B locus. Independent choices give A/B, A/b, a/B and a/b. Each route has probability (1/2) × (1/2) = 1/4. The independence assumption is needed for these four equal probabilities. [R1]", "transfer": "For AABb, list the possible gametes and their probabilities. Which two choices from AaBb disappear, and why?" }, { "id": "mi-independent-2", "concept": "Independent two-locus crosses", "prerequisites": [ "One-locus crosses" ], "prompt": "For AABb × Aabb, assume independent assortment, random fertilization and complete dominance at each locus with no interaction between the traits. What is the probability of an offspring with the A-dominant phenotype AND genotype bb?", "options": [ "1/2", "1/4", "3/4", "9/16" ], "answer": 0, "explanation": "At the A locus, AA × Aa always contributes at least one A, so P(A-dominant) = 1. At the B locus, Bb × bb gives bb with probability 1/2. Independence gives 1 × 1/2 = 1/2. For AaBb × AaBb, 9/16 describes A-dominant AND B-dominant offspring; A-dominant AND bb has probability 3/16 in that cross. Neither number answers the given AABb × Aabb cross.", "transfer": "Use the lab to find the two genotypes included in this requested outcome. What is the probability of each, and how do they add to the phenotype probability?" }, { "id": "mi-independent-3", "concept": "Independent two-locus crosses", "prerequisites": [ "One-locus crosses" ], "prompt": "A proposed inheritance model assigns an AaBb parent's gamete probabilities as AB = 0.40, ab = 0.40, Ab = 0.10 and aB = 0.10. These are stipulated probabilities, not noisy sample counts. Can the lab's equal-gamete independent-assortment model represent this distribution exactly?", "options": [ "Yes; four possible gamete names always means four equal probabilities.", "Yes; the 9:3:3:1 phenotype ratio applies to every two-locus cross.", "No; this distribution needs a model with the stated unequal gamete probabilities.", "No; the genotype AaBb is impossible." ], "answer": 2, "explanation": "The four probabilities sum to 1, but they are not the equal 1/4 probabilities assumed for AaBb in this lab. Retaining the names while replacing the weights with 1/4 would answer a different question. Linked loci are one reason independence may be unsuitable; this exercise does not diagnose a mechanism from sample counts. [R1]", "transfer": "What information would you need about the other parent's gametes before computing offspring probabilities for this unequal distribution? Explain why a larger Punnett table alone does not supply the missing weights." } ] }