Week 10 Biology Lab & Inquiry: Modeling Meiosis, Counting the Combinations

Part 1 — The Big Picture

This week you learned that meiosis makes gametes in two divisions after one round of DNA copying: meiosis I separates the homologous chromosomes and meiosis II separates the sister chromatids, leaving four haploid cells. You also learned that independent assortment in metaphase I lets each pair send either parent's copy into a gamete, so a cell with n pairs can make 2ⁿ kinds of gametes, and that crossing over in prophase I adds more. In this lab you build that idea with your hands. You cut paper chromosomes for a cell with three pairs, label one copy of each pair B and the other R, walk them through both divisions, and list every gamete the cell can make. Then you let chance do the sorting: a coin flip for each pair, 24 times, to see how a random run compares with the full list. Last, you scale the count up to a human and check a chatbot's account of your lab for mixed-up steps, swapped labels, garbled counts, and invented numbers.

Time budget: Plan for about 120 minutes.

Part 2 — The Task

Guiding question: How many genetically different gametes can a cell with three chromosome pairs make from independent assortment alone, and how close does a random run of 24 gametes come to showing every one of them?

Before you begin — hypothesis: Before you sort any chromosomes, write one hypothesis in the if… then… because… form: if a cell has three chromosome pairs and each pair can send either of its two copies into a gamete, then the cell can make a certain number of different gametes, because of a reason about how the pairs line up that you can state. Then predict how many of those gamete types will show up at least once in 24 random coin-flip trials.

Workshop data: Your own 24 random gametes from the paper model, or the illustrative fallback counts

Source: Gamete labels you record yourself at a kitchen table by flipping a coin once for each of the model cell's three pairs, 24 times, with the procedure in Part 3; if you cannot run the protocol, use the illustrative fallback counts printed in the fallback, which were constructed for this lab and are not real data.

• Rows: 24 random gametes, one per trial, summarized as 8 rows of the tally table (one row per gamete type); the setup table has 5 rows that name the parts of the model rather than data, and the doubling table has 4 rows
• Columns: gamete type written long, medium, short; tally of trials; count; and the count expected if every type were equally likely
• Unit: a count of trials out of 24

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)
• Two sheets of paper, scissors, a pen, tape, and one coin
• 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

1. Cut six paper strips: two long, two medium, and two short. On one strip of each length write B, and on the other write R. Each B and R strip of the same length is one homologous pair, so you now hold a cell with three pairs and six chromosomes. Tool: Free virtual labs and simulations (PhET, HHMI BioInteractive, Learn.Genetics), a virtual microscope, and a spreadsheet (Google Sheets or any free spreadsheet). Check: Six labeled strips in three matched pairs, long, medium, and short, with one B and one R in each pair.
2. Before you sort anything, fill in the setup table in Part 4: your if… then… because… hypothesis, your prediction, what the B and R labels stand for, and how many chromosome pairs the model cell has. 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 setup table holds a hypothesis, a prediction for the 24 trials, and the meaning of B and R.
3. Model the S phase by cutting a copy of each strip, writing the same label on it, and taping it to its original at the middle to make an X. Then run meiosis I: lay each B beside its R partner, line the three pairs up across the middle of the table, and slide the partners apart into two groups. Run meiosis II: untape every X and slide the two copies apart, making four groups of three. Tool: Free virtual labs and simulations (PhET, HHMI BioInteractive, Learn.Genetics), a virtual microscope, and a spreadsheet (Google Sheets or any free spreadsheet). Check: Twelve strips after the S phase, two groups of three taped Xs after meiosis I, and four groups of three single strips after meiosis II, each with one long, one medium, and one short strip.
4. Lay out every different gamete the cell could make, written long, medium, short, by switching which copy of each pair goes into the group. Record each one in the tally table in Part 4 until no new combination is possible. If you cannot cut paper, use the Learn.Genetics page on chromosomes, mitosis, meiosis, and fertilization to see the divisions, and list the combinations on paper. 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 list of different gamete types with no repeats, each written as three letters.
5. Run 24 random trials. In each trial flip the coin once for the long pair, once for the medium pair, and once for the short pair; heads means the B copy goes into the gamete and tails means the R copy goes in. Write the three-letter result and add a tally mark beside that type in the tally table. Tool: Free virtual labs and simulations (PhET, HHMI BioInteractive, Learn.Genetics), a virtual microscope, and a spreadsheet (Google Sheets or any free spreadsheet). Check: 24 tally marks spread across the gamete types, and a count column that adds up to 24.
6. Open a blank sheet. In cells A2 to A5 type the number of pairs 2, 3, 4, and 5, then type =2^A2 in cell B2 and fill it down to B5. In cell B7 type =2^23. Copy the results into the doubling table in Part 4. 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 B column doubles from one row to the next, and B7 shows the count for a cell with 23 pairs.
7. Model crossing over: take the long B and long R copies before meiosis II, snip the same short end off one copy of each, and swap and tape the ends. Write one sentence on what kinds of gametes this makes possible that your list did not include. Then answer the analysis questions and run the critique 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: Two long chromatids that each carry a piece of the other parent's copy, and a written note on the new combinations.

Fallback route

When to use it: Use this route if you cannot get paper, scissors, tape, or a coin, or if you cannot run the trials at home.

Use the illustrative fallback counts below, constructed for this lab and not real data, as your tally of 24 random gametes, then complete every scaffold table, analysis question, and the critique step from them and submit the same items for equal credit. Fill the empty column yourself.

This route earns the same credit as the primary route.

Illustrative fallback counts of 24 random gametes from the three-pair model, constructed for this lab, that stand in for your own coin flips.

Fallback model data

Gamete type (long, medium, short)	Tally of trials	Count	Count if every type were equally likely
BBB		3
BBR		4
BRB		2
BRR		3
RBB		3
RBR		2
RRB		4
RRR		3

Part 4 — The Scaffold

Name every part of the model before you sort, so your prediction is on record first.

Student scaffold table 1

Part of the model	Your answer
Hypothesis (if… then… because…)
Prediction: gamete types that will appear in 24 trials
What B and R stand for
Number of chromosome pairs (n) in the model cell
The process in metaphase I that sorts the copies

List each gamete type, tally your 24 random trials, and compare each count with an equal share of the trials.

Student scaffold table 2

Gamete type (long, medium, short)	Tally of trials	Count	Count if every type were equally likely

Watch what each added pair does to the number of gamete types.

Student scaffold table 3

Chromosome pairs (n)	Gamete types from independent assortment (2ⁿ)	Change from the row before
2
3
4
5

Part 5 — Analysis Questions

1. Show that your counts add up to 24, find the count you would expect for each type if all were equally likely (24 ÷ the number of types), and say how many types appeared at least once. Then use the doubling table to give the count for 4 pairs, 5 pairs, and a human's 23 pairs, writing each as 2 multiplied by itself.
2. Using your paper model, say which move separated the homologous chromosomes and which separated the sister chromatids, in order, and say how many times the DNA was copied. Then write one conclusion sentence about your hypothesis that uses supports or fails to support rather than proves.
3. Compare your 24 random gametes with the full list. Did every type appear? Were the counts equal? Explain why a random run of 24 trials rarely lands exactly on an equal share for every type, even though each type is equally likely.
4. Explain what your crossing-over snip added that the list of whole-chromosome combinations could not, and connect the variety from independent assortment, crossing over, and random fertilization to natural selection.
5. Choose one and answer it in 3–4 sentences. (a) Name one way your paper cell is simpler than a real cell, and say why the counting rule still scales to 23 pairs even though the model does not. (b) Your run had only 24 trials: say what you would expect to change in the counts with many more trials, and why.

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 10 Biology Lab & Inquiry tables above. I built a paper model of a cell with three chromosome pairs (long, medium, and short), labeled one copy of each pair B and the other R, ran it through meiosis, and then made 24 random gametes by flipping a coin once for each pair. Please do seven things. First, list every different gamete my three-pair cell can make from independent assortment alone, and give the count. Second, name the two divisions of meiosis in order, say what separates in each, and say when the DNA is copied. Third, label the parts of one duplicated chromosome and of one homologous pair in my model. Fourth, say how many genetically different gametes a human can make from independent assortment alone, with its 23 pairs, and show how you got it. Fifth, explain in which phase crossing over happens and whether it also happens in mitosis. Sixth, tell me the exact percentage of human egg cells that carry at least one crossover, with its source. Seventh, as a stretch question for next week, say what phenotype ratio a cross of two Tt parents gives.

Test the response for these likely failures:

• Chatbots sometimes say the DNA is copied again between meiosis I and meiosis II, or describe sister chromatids separating in the first division and homologs in the second.
• Chatbots often say crossing over also happens in mitosis, or describe meiosis as making two identical cells the way mitosis does.
• Chatbots sometimes give the human gamete count as 46 or as 2 × 23, and on the stretch question give the phenotype ratio of a Tt by Tt cross as 1:2:1, which is the genotype ratio.
• Chatbots often call the two arms of one duplicated chromosome homologous chromosomes, or call the B and R chromosomes of a pair sister chromatids.
• Chatbots sometimes list fewer than eight gametes, repeat one such as BRB, or explain the variety as each chromosome being cut in half, skipping the random, independent lining up of each pair.
• Asked for a percentage, chatbots often state a precise share of egg cells with a crossover and cite a study or 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; mark the stretch answer as one to check next week.

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: "My three-pair paper cell can make only 6 kinds of gametes, one for each chromosome: BBB, BBR, BRB, BRR, RBB, and BRB. In the first division of meiosis the sister chromatids come apart, and then the cell copies its DNA again so the homologous chromosomes can separate in the second division. The two arms of each taped X are homologous chromosomes. A human, with 23 pairs, can make 2 × 23 = 46 kinds of gametes. Crossing over happens in mitosis too, which is why skin cells differ from each other, and exactly 63 percent of human eggs carry a crossover, as a study shows. As a preview of next week, a cross of two Tt parents gives a 1:2:1 phenotype ratio." Mark it up: quote each flawed sentence, name what is wrong (a step out of order, a mitosis and meiosis mix-up, a garbled count or ratio, a mislabeled structure, an over-simplified mechanism, or an invented figure), cite the evidence from your tables or this week's chapter, and write a corrected sentence beneath it; for the preview sentence, say which week will check it. This route assesses the same objectives (Objective 1 and Objective 5) 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 three completed scaffold tables, filled from your own model and coin flips or the illustrative fallback counts
• 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 modeling meiosis: three completed tables (the named parts of the model, the gamete list with your 24-trial tally and the equal-share comparison, and the doubling table up to a human), 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 model setup	A falsifiable if… then… because… hypothesis and a prediction for the 24 trials appear before any sorting, the meaning of B and R is stated, the number of pairs is given, and independent assortment is named as the sorting process.	A hypothesis appears but is not falsifiable or lacks a prediction, or the labels, the number of pairs, or the sorting process is missing or wrong.	No hypothesis, or the parts of the model are not named.
Gamete list, tally, and doubling table	The list holds every gamete type with no repeats, the 24 trials are tallied from the student's own flips or the fallback counts with a total that sums to 24, the equal-share count is worked out, and the doubling table is correct through 5 pairs with the human count added.	The tables are filled, but the list repeats or misses a type, the total or equal share is wrong, or a doubling-table value is wrong or unexplained.	No list or tally is recorded, or the counts are invented rather than flipped or taken from the fallback.
Meiosis analysis and sources of variation	Questions 1 to 4 are answered accurately: the counts are checked and scaled with the doubling rule, meiosis I is shown separating homologs and meiosis II separating sisters after one copying round, the conclusion uses supports or fails to support, chance variation in 24 trials is explained, and crossing over and random fertilization are tied to natural selection.	The questions are attempted, but one or two answers put the divisions out of order, swap homologs and sisters, give the human count as 23 or 46, place crossing over in mitosis, or claim the result proves the hypothesis.	The analysis questions are missing or do not address the model.
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, the stretch answer is marked to check later, 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 model	The chosen reflection option is answered in 3–4 sentences that tie a specific simplification of the paper cell, or the small number of trials, to a concrete statement about what the model can and cannot show.	The reflection is answered but stays general or names no specific consequence.	No reflection is submitted.

Quality Gate

• Every count in the tally table comes from your own coin flips or the printed fallback counts, never from memory or a chatbot.
• The gamete list has no repeats, and each count total shows its sum.
• The hypothesis was written before any sorting and has the if… then… because… form.
• Meiosis I is shown separating homologs and meiosis II separating sister chromatids, with the DNA copied once.
• No measurement, percentage, 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.