Week 12 — Blends, Blood Types, and Carriers: The Patterns of Inheritance Report — Traditional alternative (no AI)

Instructors: publish this instead of the adaptive version if you prefer, and unpublish or delete the adaptive one.

Assignment 11 of the term — work three non-Mendelian crosses into counts, explain what each heterozygote shows, and tell a friend why a family's sons can show a trait their fathers do not.

This week you learned three ways Mendel's simple rule bends: a heterozygote can be a blend, a gene can have more than two alleles in a population, and a gene on the X chromosome shows in a male with one copy. In this assignment you work four short problems, interpret each one, and explain to someone who has never studied biology why a family's affected sons get the allele from their mothers. This week's lecture tutorial, quiz, discussion, and Biology Lab & Inquiry practise the same ideas from other angles. It builds on Week 11's Punnett squares and product rule, which work the same way here.

The task

The non-Mendelian crosses are the discipline's canonical crosses with the arithmetic shown. In each problem below, the total number of offspring or children is illustrative, chosen for this assignment, and the probabilities come from the crosses:

• RW × RW (two pink snapdragons): 1 red : 2 pink : 1 white, so P(pink) = 1⁄2;
• the ABO gene: three common alleles, Iᴬ, Iᴮ, and i;
• Iᴬi × Iᴮi (a type A parent and a type B parent): AB, A, B, and O, each 1⁄4;
• XᴬXᵃ × XᴬY (a carrier mother and an unaffected father): 1⁄2 of sons affected, 0 of daughters affected, and 1⁄4 of all children affected.

Work these four problems, showing your arithmetic:

1. Two pink snapdragons (RW × RW) give P(pink) = 1⁄2. Among 100 illustrative offspring of such crosses, how many pink offspring do the odds predict?
2. The ABO gene has three common alleles, and each person carries two. Counting the 3 homozygous genotypes (IᴬIᴬ, IᴮIᴮ, ii) and the 3 heterozygous genotypes (IᴬIᴮ, Iᴬi, Iᴮi), how many ABO genotypes are there?
3. A type A parent (Iᴬi) and a type B parent (Iᴮi) each pass i with probability 1⁄2, so P(O) = 1⁄2 × 1⁄2 = 1⁄4. Across 80 illustrative children of such couples, how many type O children do the odds predict?
4. In the carrier cross XᴬXᵃ × XᴬY, 1⁄4 of all children are affected by the X-linked recessive trait. Across 60 illustrative children of such couples, how many affected children do the odds predict?

Beside each answer, add one brief interpretation:

• Problem 1: explain incomplete dominance as a blend partway between the parents, and explain why the color ratio for RW × RW is 1 red : 2 pink : 1 white, matching the genotype ratio, rather than 3:1.
• Problem 2: explain why Iᴬ and Iᴮ are codominant, naming what a type AB red blood cell carries, and explain why type O is common even though i is recessive.
• Problem 3: explain how two parents who show A and B can have a type O child, and name the probability rule that gives P(O).
• Problem 4: explain why every affected child in the carrier cross is a son, using where a son's X comes from and what hemizygous means, and say why a male cannot be a carrier.

Explain it to a non-expert

A friend is drawing a family chart for a made-up trait and notices that, across three generations, only sons show it and no father who shows it has passed it to his son. The friend asks, "Does that mean the dads pass it down?" Write a 3–5 sentence message that explains, in everyday words, where a son's X chromosome comes from and how a mother can carry the allele without showing it, connects it to the carrier cross, and names one limit, including that a small family chart cannot rule out every other pattern and that the counts in your report are illustrative. Explain any technical term in everyday words. More than one good answer is possible.

For a different, ungraded example, imagine a friend asking why a sprint leaves your legs burning when a slow jog does not. Model answer: "Your muscles run on a fuel your cells remake from food, and the best way to remake it needs oxygen. In a sprint your muscles need fuel faster than your blood can bring oxygen, so they switch to a quick backup that works without it. That backup makes much less fuel, so you tire fast. This explains why a sprint feels harder, but it does not tell you exactly how long you can keep it up, which differs from person to person."

Use that pattern for your friend's family chart, with your own wording and evidence.

Show your arithmetic. A reader should be able to reproduce every number you report from the totals and probabilities in the problems without guessing which values or steps you used.

Deliverables

Submit a single report containing:

• the four answers, each with the arithmetic shown and the brief interpretation the task names for that problem;
• your message to your friend, explaining in everyday words where a son's X chromosome comes from and how a mother can carry the allele without showing it, with one limit; and
• a one-line restatement of the probabilities and totals you used, so your results are reproducible.

Keep it to roughly one page. Clear and correct beats long.

Choose how you show it. Present your report as written text, or as a recorded audio or video explanation of about three minutes with a transcript, or as labelled hand-drawn Punnett squares with a short note. Every form is graded by the same scoring criteria. Submit in any accessible file type or as a link; a recorded response may be submitted as audio or video with a transcript, or as text.

How you'll be graded

The full analytic rubric is attached to this assignment in Canvas.

Academic integrity and AI use

This version is designed to be completed without AI: do the arithmetic, the interpretations, and the writing yourself, without a chatbot or other AI tool. You may use a calculator, a spreadsheet, or paper Punnett squares. Submitting AI-generated work as your own, or copying another student's work, is an integrity violation under the course policy.

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