Week 15 · Biology Lab & Inquiry

Week 15 Biology Lab & Inquiry: Whose DNA Is It? A Virtual Gel

Introduction to Biology Free sample edition

Part 1 — The Big Picture

This week you learned that PCR copies a trace of DNA and gel electrophoresis then sorts the copies by size: DNA is negatively charged, so it runs from the wells toward the positive end, and smaller fragments slip through the gel and travel farther. You also learned that DNA profiling compares band patterns, and that one band that does not line up rules a person out more firmly than a matching pattern rules a person in. In this lab you first run a gel yourself in the Learn.Genetics virtual lab, watching where the DNA starts, which way it moves, and how the bands spread out. Then you read a printed illustrative gel the way a crime lab would: you size each band against a ladder, compare an evidence sample with three people, and decide who is excluded and who is not. Finally you check a chatbot's account of your lab and catch where it scrambles an order, mislabels a part of the gel, oversimplifies what a match means, swaps mitosis for meiosis, garbles a ratio, or invents a number.

Time budget: Plan for about 120 minutes.

Part 2 — The Task

Guiding question: Which of Persons A, B, and C can be excluded as the source of the evidence sample on the printed illustrative gel, and why is an exclusion a firmer conclusion than a match?

Before you begin — hypothesis: Before you compare the lanes, write one hypothesis in the if… then… because… form: if the evidence sample came from one of the three people, then that person's bands will line up with the evidence bands at every position, because a reason about how a gel sorts DNA that you can state. Then predict whether a single band that does not line up is enough to exclude a person.

Workshop data: Your own run of the Learn.Genetics virtual gel, plus the printed illustrative evidence gel

Source: Your observations come from your own run of the Learn.Genetics gel electrophoresis virtual lab; the band distances in the evidence gel table are an illustrative dataset constructed for this lab, not real case data.

Rows: 5 lanes on the printed evidence gel (a size ladder of five bands, an evidence sample, and Persons A, B, and C), shown as 5 rows in the evidence gel table; the observation table from your simulation run has 4 rows and the matching table has 3 rows
Columns: lane, band 1 distance from the wells, and band 2 distance from the wells, in millimeters
Unit: distance in millimeters (mm) from the wells, read against a size ladder labelled in base pairs (bp)

Part 3 — Materials & Procedure

Tools and materials

Free virtual labs and simulations (PhET, HHMI BioInteractive, Learn.Genetics), a virtual microscope, and a spreadsheet (Google Sheets or any free spreadsheet)
A computer or tablet with a web browser that opens the Learn.Genetics Gel Electrophoresis virtual lab
A document or notebook for your written answers

Ways of working

virtual-simulation-inquiry
at-home-protocol-and-data-table
figure-and-diagram-interpretation

Procedure

Open the Learn.Genetics Gel Electrophoresis virtual lab in your web browser. Read each screen and press FORWARD to move on; the lab runs in a browser player, so give it a moment to load. Tool: Free virtual labs and simulations (PhET, HHMI BioInteractive, Learn.Genetics), a virtual microscope, and a spreadsheet (Google Sheets or any free spreadsheet). Check: The lab's opening screens explain what a gel does, then list five steps: make the gel, set up the gel apparatus, load the DNA sample, hook up the current and run the gel, and stain the gel and analyze the results.
Before you run anything, fill in the first table in Part 4: your hypothesis, your prediction, what you compare, and what stays the same across the lanes. Tool: Free virtual labs and simulations (PhET, HHMI BioInteractive, Learn.Genetics), a virtual microscope, and a spreadsheet (Google Sheets or any free spreadsheet). Check: The first table has an if… then… because… hypothesis and a prediction about a single band that does not line up.
Work through the lab's five steps in order, following the instruction in the box under each screen. As you go, note where the DNA samples are loaded, which electrode is negative and which is positive, and which way the DNA moves when the current runs. Tool: Free virtual labs and simulations (PhET, HHMI BioInteractive, Learn.Genetics), a virtual microscope, and a spreadsheet (Google Sheets or any free spreadsheet). Check: A finished, stained virtual gel and notes on the loading end, the two electrodes, and the direction of travel.
Fill in the simulation observation table in Part 4 from your own run: where the samples started, which way they moved, which bands ended up farthest from the wells, and what that tells you about their size. Tool: Free virtual labs and simulations (PhET, HHMI BioInteractive, Learn.Genetics), a virtual microscope, and a spreadsheet (Google Sheets or any free spreadsheet). Check: Four observations from your own run, each in one short sentence.
Now read the printed illustrative evidence gel in Part 4. Use the size ladder to give each band a size in bp: a band at the same distance as a ladder band is that ladder band's size. Optionally, type the five ladder sizes into cells A2 to A6 of a spreadsheet and check that =MAX(A2:A6) returns 3200 and =MIN(A2:A6) returns 200, the two sizes you divide in analysis question 1. Tool: Free virtual labs and simulations (PhET, HHMI BioInteractive, Learn.Genetics), a virtual microscope, and a spreadsheet (Google Sheets or any free spreadsheet). Check: Every band in the evidence, Person A, Person B, and Person C lanes has a size in bp.
Fill in the matching table: for each person, count how many of the evidence sample's two bands line up, and write whether that person is excluded or not excluded. Then answer the analysis questions in Part 5 and run the critique step in Part 6. Tool: Free virtual labs and simulations (PhET, HHMI BioInteractive, Learn.Genetics), a virtual microscope, and a spreadsheet (Google Sheets or any free spreadsheet). Check: Three rows, each with a count of matching bands out of 2 and a call of excluded or not excluded.

Fallback route

When to use it: Use this route if the Learn.Genetics virtual lab will not load on your device or network.

Use the illustrative fallback observations below, constructed for this lab, in place of your own run: copy them into the simulation observation table, then complete the evidence gel table, the matching table, every analysis question, and the critique step from them, and submit the same items for equal credit.

This route earns the same credit as the primary route.

Illustrative fallback observations of a virtual gel run, constructed for this lab, that stand in for your own run.

Fallback model data
Observation	What the run showed
The end of the gel where the DNA samples were loaded	The wells, at the negative end
The electrode the DNA moved toward, negative or positive	The positive electrode
The bands that ended up farthest from the wells	The bands of the shortest strands
What distance from the wells tells you about a fragment's size

Part 4 — The Scaffold

Name every part of the test before you compare lanes, so the comparison is fair from the start.

Student scaffold table 1
Part of the test	Your answer
Hypothesis (if… then… because…)
Prediction: is one band that does not line up enough to exclude a person?
What you compare between lanes
Two things that stay the same for every lane on one gel

Record what your own run of the virtual lab showed, in one sentence per row.

Student scaffold table 2
Observation	What your run showed
The end of the gel where the DNA samples were loaded
The electrode the DNA moved toward, negative or positive
The bands that ended up farthest from the wells
What distance from the wells tells you about a fragment's size

Read the printed illustrative evidence gel: the ladder bands are 3,200, 1,600, 800, 400, and 200 bp at 12, 24, 36, 48, and 60 mm from the wells. Give each sample band its size.

Student scaffold table 3
Lane	Band 1 distance from the wells (mm)	Band 2 distance from the wells (mm)
Evidence sample	12	48
Person A	24	48
Person B	12	48
Person C	12	60

Compare each person with the evidence sample and make the call.

Student scaffold table 4
Person	Bands that line up with the evidence (out of 2)	Excluded or not excluded	The band that settles it
Person A
Person B
Person C

Part 5 — Analysis Questions

Show the division for the size gap between the largest and smallest ladder bands, and show how many millimeters farther a band travels each time the fragment size is cut in half, using two pairs of neighboring ladder bands.
From your own run of the virtual lab, which way did the DNA move, and which bands traveled farthest? Explain both observations using the charge on DNA and the size of the fragments.
Which people are excluded and which is not excluded? Write one conclusion sentence that uses supports or fails to support rather than proves, and explain why one band that does not line up is a firmer call than two bands that do.
A real crime lab starts with only a trace of DNA. Explain which tool it uses before running a gel, in what order the three steps of each round run, and why PCR and gel electrophoresis are two different tools rather than one.
Choose one and answer it in 3–4 sentences. (a) This gel compares only two bands per lane: explain why so few bands limits how strongly a match can point to one person, and what more evidence would help. (b) The printed gel is illustrative and the virtual lab is a model: name one way a real gel could be harder to read than this one, and how a lab could guard against that problem.

Part 6 — AI-Critique Moment

Choose one equal-credit critique route. Route A: ask an approved AI tool to critique your completed work, then check its response against your own evidence. Route B is the no-AI equivalent printed below.

Approved tools: Claude, Gemini, ChatGPT, Grok, Microsoft Copilot.

Prompt to paste:

I've pasted my completed Week 15 Biology Lab & Inquiry tables above. I ran the Learn.Genetics gel electrophoresis lab and then read a printed illustrative gel with a size ladder of 200, 400, 800, 1,600, and 3,200 bp, an evidence sample, and three people, A, B, and C. Please do six things. First, put PCR and gel electrophoresis in the order a crime lab uses them, and give the three steps of one PCR round in order. Second, say which end of a gel the wells sit at, the negative end or the positive end, and which ladder band travels farthest from the wells. Third, say whether Person B's matching band pattern proves the evidence came from Person B. Fourth, say which kind of cell division makes the eggs and sperm that would carry a germline edit to a child. Fifth, if a person carries one edited copy of a gene and one unedited copy, what fraction of that person's eggs or sperm carry the edited copy? Sixth, tell me the exact chance that two unrelated people share this band pattern, with its source.

Test the response for these likely failures:

Chatbots sometimes say the gel runs first to find the DNA and PCR copies it afterward, or list the PCR steps as anneal, denature, extend.
Chatbots sometimes put the wells at the positive end, or say the largest ladder band travels farthest.
Chatbots often say a matching band pattern proves the evidence came from that person.
Chatbots sometimes say eggs and sperm are made by mitosis, or that a germline edit spreads to children through mitosis.
Chatbots sometimes say all of the gametes, or one in four, carry the edited copy.
Asked for the chance that two unrelated people share the pattern, chatbots often state a precise number and cite a source that was never given.

Write 3–5 sentences naming one thing the chatbot got right and at least two places it went wrong or overreached, quoting its words and correcting each with evidence from your own tables or this week's chapter.

Equivalent route (no AI required)

No AI account is required for this lab. Instead of the chatbot, critique this flawed analysis, printed here in full: "The lab ran the gel first to find the DNA and then used PCR to copy it, and each PCR round goes anneal, denature, extend. The wells sit at the positive end, and the 3,200 bp band traveled farthest because big pieces are heavier. Person B's bands match the evidence, which proves the evidence came from Person B. If Person B had a germline edit, it would reach Person B's children through mitosis, and every one of Person B's sperm or eggs would carry the edited copy. Two unrelated people share a pattern like this about 1 time in 2,000, according to a study." Mark it up: quote each flawed sentence, name what is wrong (a mis-ordered process, a mislabeled part of the gel, an over-simplified mechanism, a mitosis-for-meiosis swap, a garbled ratio, or an invented figure), cite the evidence from your tables or this week's chapter, and write a corrected sentence beneath it. This route assesses the same objectives (Objective 7 and Objective 8) as the chatbot critique, takes comparable effort (about 30 minutes and 200–300 words), is scored by the same scoring criteria for the same credit, and its own submission artifact is the marked-up flawed analysis, posted in place of the chatbot share link and report.

Part 7 — What to Submit

All four completed scaffold tables, filled from your own run or the illustrative fallback observations and from the printed evidence gel
Written answers to all five analysis questions
The chatbot critique report with its share link, or the equivalent route's marked-up flawed analysis

Deliverable:

A short Biology Lab & Inquiry report on reading a DNA gel: four completed tables (the named parts of the test, your observations from the virtual lab, the band sizes on the printed evidence gel, and the excluded-or-not calls for Persons A, B, and C), written answers to five analysis questions, and a critique of a chatbot's account of your lab, or, on the equivalent route, a marked-up correction of the printed flawed analysis. 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. Choose a written, recorded, or visual form for your answers; every form is graded by the same scoring criteria.

Rubric

The rubric below shows how each submitted part is evaluated; bands are full, partial, or none.

Workshop evaluation criteria
Criterion	Full	Partial	None
Testable hypothesis and the parts of the comparison	A falsifiable if… then… because… hypothesis and a prediction about a single mismatched band appear before the lanes are compared, and what is compared and what stays the same across lanes are named.	A hypothesis appears but is not falsifiable or lacks the prediction, or what is compared or what stays the same is missing.	No hypothesis, or the parts of the comparison are not named.
Completed observation, band-size, and matching tables	The observation table comes from the student's own run or the fallback, every band on the printed gel is given its correct size from the ladder, and each person's count of lined-up bands and excluded-or-not call is correct, with the settling band named.	The tables are filled, but one or two band sizes, counts, or calls are wrong, or the settling band is not named.	No tables are filled, or the observations and sizes are invented rather than read from the run, the fallback, or the printed gel.
Gel analysis: size, direction, exclusion, and the order of the tools	Questions 1 to 4 are answered accurately: the size gap and distance step show their arithmetic, travel is explained by charge and size, the conclusion uses supports or fails to support and explains why an exclusion is firmer than a match, and PCR is placed before the gel with its steps in order.	Some of questions 1 to 4 are accurate, but larger fragments are said to travel farther, a match is treated as proof, or PCR and the gel are blurred or put out of order.	Questions 1 to 4 are missing or inaccurate throughout.
Critique of the chatbot or of the printed flawed analysis	On either route, at least two errors are quoted and corrected with evidence from the student's own tables or the chapter, and one correct point is acknowledged; both routes earn this band equally.	On either route, errors are named but corrected without evidence, or only one error is caught.	No critique appears, or pasted output is submitted without any checking.
Reflection on the limits of the evidence	The chosen reflection option is answered in 3–4 sentences that tie a specific limit of the gel or the model to a concrete change in the evidence or in what can be claimed.	The reflection is answered but stays general or names no specific change.	No reflection is submitted.

Quality Gate

Every observation comes from your own run of the virtual lab or the printed fallback observations, never from memory or a chatbot.
Every band size is read from the ladder on the printed gel, and each size gap or distance step shows its division or subtraction.
The hypothesis was written before the lanes were compared and has the if… then… because… form.
Each person is called excluded or not excluded with the band that settles it, and no match is called proof.
PCR is placed before the gel, and the steps of a PCR round are in the order denature, anneal, extend.
No measurement, percentage, probability, study, or source is invented anywhere in the submission.
The critique quotes the chatbot or the flawed analysis and corrects at least two errors with evidence from your tables or the chapter.

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