Week 15 — Gels and Typos: The DNA Profiling and Mutation Report

Assignment 14 of the term — read the virtual gel, follow two typos through Gene 1, choose the right tool for a job, and explain to a relative what a DNA match does and does not prove.

This adaptive assignment uses a coaching dialogue to help you turn a first attempt into a clear, evidence-based report on this week's biotechnology and mutation ideas. You remain the author. The coach asks questions, checks the reasoning you show, and waits for you to revise before it produces the required report. This week's lecture tutorial, quiz, discussion, and Biology Lab & Inquiry practise the same ideas from other angles; this assignment is where you put the virtual gel, Gene 1, and the biotechnology toolkit together. It builds on Week 14's codon reading, which is how you tell what a typo does to a protein.

This is the last assignment of the course, so it also asks you to choose among the tools you have learned and say why one fits a job better than another.

The task

The virtual gel is an illustrative dataset constructed for this course (not real data). Its size ladder has bands at 500, 1,000, 2,000, and 4,000 bp (base pairs), and smaller fragments travel farther from the wells. Three sample lanes sit beside the ladder:

• the crime-scene lane, with bands at 500, 2,000, and 4,000 bp;
• Suspect 1, with bands at 1,000, 2,000, and 4,000 bp;
• Suspect 2, with bands at 500, 2,000, and 4,000 bp.

Gene 1 from Week 14 returns too: its mRNA is 5′-AUG GCU UAU UGA-3′, which reads Met–Ala–Tyr and then stop.

Work these four problems, showing your arithmetic:

1. On the illustrative virtual gel, the size ladder's largest band is 4,000 bp and its smallest band is 500 bp. How many times larger is the largest band than the smallest?
2. Gene 1's mRNA, 5′-AUG GCU UAU UGA-3′, has 12 bases. If the first base after AUG is deleted, how many bases remain?
3. On the illustrative virtual gel, each ladder band is twice the size of the band below it, and the smallest band is 500 bp. What size, in bp, is the band two steps above the smallest?
4. On Gene 1's mRNA, the codon UAU at codon position 3 becomes the stop codon UAA. Counting AUG as codon position 1, how many amino acids does the shortened protein carry?

Beside each answer, add one brief interpretation:

• Problem 1: explain why the 4,000 bp band sits nearest the wells, and choose the tool: a lab has only a trace of DNA from a scene, so which tool would it use to get enough DNA before running this gel, and why do gel electrophoresis alone and CRISPR-Cas9 fit that job less well?
• Problem 2: name the kind of mutation, and regroup the remaining bases in threes from AUG to explain what happens to every codon after the deletion and to the UGA stop.
• Problem 3: read the crime-scene lane against both suspects, say which suspect matches and which is excluded, and explain why one band that differs is a firmer call than a match.
• Problem 4: name the kind of mutation, and contrast it with the change GCU to GAU on the same gene.

Explain it to a non-expert

A relative who has been called for jury duty asks, "If the DNA at a crime scene matches someone, does that prove they did it?" Write a 3–5 sentence message that explains, in everyday words, what a matching band pattern does and does not show, connects it to the virtual gel, and names one limit, including that the gel's numbers are illustrative rather than real case data. Explain any technical term in everyday words. More than one good answer is possible.

For a different, ungraded example, imagine a friend asking why bread dough rises. Model answer: "Bread dough rises because yeast, a tiny living fungus, breaks down sugar without oxygen and gives off carbon dioxide gas. The gas gets trapped in the stretchy dough and puffs it up, the same way air fills a balloon. Biologists call this alcoholic fermentation. It explains the rise, but it does not tell you exactly how big a loaf will get, which depends on the yeast, the sugar, the warmth, and the time."

Use that pattern for your relative's question, with your own wording and evidence.

Part 1 — Student instructions

1. Draft all four answers, the four brief interpretations, and your message to your relative before opening a chatbot.
2. Open any course-approved chatbot. Copy the entire Coach Prompt box, including its first and last marker lines, and paste it as one message. The coach will ask for your draft and then work one question at a time.
3. Answer in your own words. Show calculations when asked. Use the coach's feedback to revise at least one calculation or explanation, even if your first attempt was correct.
4. Continue until the prompt's exit condition is met.
5. Save the chat's share link and copy the final report exactly as the coach gives it.

The chatbot is a coach, not a ghostwriter. It must draw out your reasoning rather than write the report for you.

Coach Prompt

COPY EVERYTHING BELOW THIS LINE
ROLE: You are a careful learning coach for an introductory biology course. Draw out and challenge MY thinking about this week's gel electrophoresis, mutations, and biotechnology tools. Do not write my assignment for me, do not invent work I did not show, and never invent a measurement, a study, a percentage, a codon meaning, or a real case.

ASSIGNMENT: Work through these four problems in order, one at a time. Do not invent, replace, or reorder a problem. The data: the virtual gel, an illustrative dataset constructed for this course (not real data). Ladder bands at 500, 1,000, 2,000, and 4,000 bp (base pairs); smaller fragments travel farther from the wells. Crime-scene lane: 500, 2,000, and 4,000 bp. Suspect 1: 1,000, 2,000, and 4,000 bp. Suspect 2: 500, 2,000, and 4,000 bp. Gene 1's mRNA is 5'-AUG GCU UAU UGA-3', which reads Met-Ala-Tyr, then stop. Codon meanings to use: AUG = Met, GCU = Ala, GAU = Asp, UAU = Tyr, and UAA, UAG, UGA = stop.
PROBLEM P1: On the illustrative virtual gel, the size ladder's largest band is 4,000 bp and its smallest band is 500 bp. How many times larger is the largest band than the smallest?
PROBLEM P2: Gene 1's mRNA, 5'-AUG GCU UAU UGA-3', has 12 bases. If the first base after AUG is deleted, how many bases remain?
PROBLEM P3: On the illustrative virtual gel, each ladder band is twice the size of the band below it, and the smallest band is 500 bp. What size, in bp, is the band two steps above the smallest?
PROBLEM P4: On Gene 1's mRNA, 5'-AUG GCU UAU UGA-3', the codon UAU at codon position 3 becomes the stop codon UAA. Counting AUG as codon position 1, how many amino acids does the shortened protein carry?
After the four answers, I must briefly interpret each one: for P1, why the 4,000 bp band sits nearest the wells, plus a tool choice: which tool a lab would use to get enough DNA from a trace sample before running the gel, and why gel electrophoresis alone and CRISPR-Cas9 fit that job less well; for P2, the kind of mutation, plus what happens to every codon after the deletion and to the UGA stop when the bases are regrouped in threes from AUG; for P3, which suspect matches and which is excluded, plus why one band that differs is a firmer call than a match; for P4, the kind of mutation, plus a contrast with the change GCU to GAU. I must then write a 3-5 sentence message to a relative called for jury duty, explaining in everyday words what a matching DNA band pattern does and does not show, connected to the virtual gel, and naming one limit, including that the gel's numbers are illustrative. I must explain technical terms in everyday words.

SCORING CRITERIA: Score only evidence I supply: correct computations (40 points), biological reasoning (32 points), clarity for a non-expert reader (16 points), and showing work so it can be checked (12 points). For each of P1-P4, give 2, 1, or 0 evidence units per criterion; one unit is worth 5 computation points, 4 reasoning points, 2 clarity points, or 1.5 showing-work points. Sum all four problems within each criterion. Count my tool choice only with P1, and my message to my relative only with P4, not again with the other problems.
COMPUTATION UNITS: A correct size ratio, base count, band size, or amino-acid count = 2; the right values and operation with only an arithmetic slip = 1; a missing result or the wrong values or operation = 0. Do not penalize an alternative valid method, such as listing the ladder bands in order and counting steps, or equivalent correct notation.
REASONING UNITS: For P1-P3 separately, an interpretation that meets both parts named for that problem = 2; exactly one part = 1; neither = 0. For P4, BOTH an accurate nonsense-versus-missense explanation AND a relative's message that says a match does not by itself prove who left a sample, in everyday words, and names a limit = 2. If full P4 evidence is absent but at least one accurate substantive part appears, give 1. No accurate reasoning = 0; saying bigger fragments travel farther, saying PCR sorts DNA, calling a new stop codon missense, saying a deletion changes only one amino acid, or calling a match proof is not accurate. An arithmetic slip alone is not a reasoning error.
CLARITY UNITS: For each problem, labeled evidence understandable to someone new to biology, with technical terms explained = 2; intelligible evidence that needs rereading because of ambiguity or jargon = 1; absent or unintelligible evidence = 0. Include the relative's message with P4 if submitted. Missing reasoning alone does not lower clarity for otherwise clear submitted work.
SHOWING-WORK UNITS: For each problem, checkable values and steps = 2; a relevant but incomplete value or step = 1; a result alone or no method = 0. A visible method stays checkable despite an arithmetic slip.

Do NOT invent grading rules.

DIALOGUE RULES: Ask exactly one question per message and wait for my answer. Start by asking for my complete first attempt. Build each next question from my exact words. Probe an unsupported claim and ask me to examine its evidence. Keep the conversation focused on questions rather than completed work.

ENGAGEMENT GUARDS: A greeting, copied prompt, yes/no reply, or one-word answer is not a substantive exchange. Do not flatter or accept agreement as evidence. Praise only a concrete move I made. If evidence is missing, say what is missing and ask for it. Require a real revision plus a short reflection on why the revision is better. Do not issue the report early.

EXIT CONDITION: Continue until at least five substantive exchanges have occurred AND I have supplied all four answers and their brief interpretations AND written my message to my relative AND revised at least one calculation or explanation AND reflected on the revision. Stop only after whichever requirement happens last.

REPORT: After the exit condition is satisfied, output exactly these labelled lines in this order. Replace X with the exact earned score; it may end in .5 and must not be rounded to a whole number. Base every line only on evidence in this chat; write "Not supplied" for missing evidence and never raise the score for polished chatbot prose.
STUDENT'S SCORE: X/100
EVIDENCE FOR THE SCORE: [specific evidence from my calculations and reasoning]
REVISION MADE: [what I changed and why]
STRENGTH: [one earned strength]
NEXT STEP: [one concrete improvement]
Then tell me to submit this report, my revised DNA profiling and mutation report, and the share link.
COPY EVERYTHING ABOVE THIS LINE

Deliverables

Submit these three items in the assignment entry:

• your revised DNA profiling and mutation report with all four answers, their brief interpretations, your tool choice, and your message to your relative — written, or recorded as audio or video with a transcript, or as a labelled hand-drawn gel with a short note; every form is graded by the same scoring criteria;
• the coach's five-line report; and
• the conversation share link.

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.

Equivalent route (no AI required)

This route assesses the same Week 15 skills — reading a gel by size, matching or excluding a DNA profile, classifying a frameshift and a nonsense mutation on Gene 1, choosing the right biotechnology tool for a job, and explaining a DNA match honestly to a non-expert — for comparable time and effort, about 60 to 90 minutes, the same as the coached route. Complete the same four problems, the four brief interpretations, the tool choice, and the message to your relative. Then audit your own first draft against the attached scoring criteria, criterion by criterion, and write a second draft. Add a 150–200 word revision memo that names one calculation or explanation you changed, the evidence that prompted the change, and one question you still have. Submit the revised report, your completed criteria checklist, and the revision memo in the assignment entry; together they replace the share link and the coach's report. This route uses the same scoring criteria and the same points, with no penalty for choosing it.

How you'll be graded

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

Looking ahead to the final

The cumulative final comes in Week 16, the finals week. Choosing a tool by its job, as you did in Problem 1, is the same move the final asks for across the whole course: name what a process or tool does, put its steps in order, and say where each one happens. To prepare, use the final study guide, the Final Practice Exam, and the exam-prep tutorial in the finals-week module.

Academic integrity and AI use

The calculations, reasoning, revision, and final report must be your own. Do not ask the chatbot to create the assignment or add evidence you did not produce. Submit an honest share link from your own dialogue. The equivalent route keeps the same workload and evidence and requires no AI account.

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