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A Mini-Lesson


Doing it on the Table



Larry Flammer

Click Here for PDF copy of this Lesson






This activity (lab) is designed to help students to learn the critical distinctions between what happens to chromosomes during mitosis vs meiosis. Students manipulate pipe-cleaner chromosomes on a template showing stages of mitosis with one pair of chromosomes until approved by the teacher. Then they repeat the exercise for meiosis until approved. After each phase, students draw in chromosomes on a summary sheet, then help other students. An application phase asks students to show the same thing using two pairs of chromosomes. Students who think they understand the critical distinctions and essential functions of these two processes going in, usually discover that it's not quite what they thought, and come out of this with a sharper understanding. This is best used as a Formative Assessment tool.


In meiosis, replicated homologous chromosomes pair off during the first division, then these separate from each other, assuring that one member of each pair of chromosomes goes into two separate cells. Replicates separate in the second division. In mitosis, there is no pairing of replicated homologous chromosomes.

Meiosis provides a mechanism that prevents doubling and re-doubling of chromosome number with every generation, and also provides a mechanism that adds to variation with every generation (from crossing over and recombination).


Sets of pipe cleaner chromosomes, one set for each student (or team of 2)
Teacher Directions (read this for details)
Template for Mitosis (one page)
Template for Meiosis (two pages)
Red and blue pencils
Keys for teacher:
Worksheet Key
Summary Key 1 (for 1 pair of chromosomes)
Summary Key 2 (for 2 pairs of chromosomes)


Worksheet: "Mitosis & Meiosis: On the Table" back to back with...
Mitosis-Meiosis Summary sheet
Extra M-M Summary sheet


See Teacher Directions for details

When I taught college prep biology, I introduced mitosis as a fundamental part of basic cell reproduction (in my Reproduction unit). We observed video clips in time-lapse so they could see the whole process of mitosis as an orderly process of nuclear duplication and separation (followed by cytoplasmic division or cytokinesis). Then they searched for and drew key phases of mitosis in onion root tips.

Later in my Repro unit, as part of my intro to sexual reproduction, I introduced Meiosis as primarily a means of preventing the redoubling of chromosomes (following fertilization) for every generation. In addition, meiosis provides ways for increased variation (random assortment, crossing over, and fertilization--from different lines of ancestry: male and female). After introducing meiosis, I developed a lab experience in which they were expected to manipulate pipe-cleaner chromosome models showing key features of mitosis, with every student getting approved for that, then showing key features of meiosis, and getting approved for that. [See my "Mitosis & Meosis: Doing it On the Table" lab]. It's a wild lab, with me rushing around the room to check out individual efforts, while students work independently and interactively on showing those distinctive features, a la short, simple set of rules.

My intro to genetics followed my reproduction unit, and the connection to meiosis was how the chromosomes assorted, with members of each pair coming together (synapsis), then separating, creating haploid (monoploid) cells from diploid cells, with each pair of chromosomes represented by one of its members going into each haploid cell. Haploid is not just any half number of the total chromosome number in diploid cells, but rather one member of each pair, making one set. It had already been established in my introduction to meiosis that it accomplishes the shift from 2n to n (2 sets to 1 set) of chromosomes in a cell, while fertilization involves n (1 set) in each gamete, typically, coming together to produce 2n (2 sets) in the zygote, typically. So, (memory device:) "miTosis mainTains" the chromosome number. "MeiOsis LOwers" the number. This understanding is important for recognizing the role that chromosomes play in X-linked traits and male-female determination of offspring.

Prepare multiple sets of pipe-cleaner chromosomes, as per directions (enough for each student in a class)
Prepare desktop templates of mitosis and meiosis (1 set for each student) (could be laminated or placed in plastic sleeves for re-use)
Run off Worksheet - Summary and extra summary pages for all students to work on.

This lesson is best done after students have at least read about mitosis and meiosis, and/or seen a film, video, or online animation showing these two processes. Mitosis may have been studied earlier in the context of cell studies, or simple cell reproduction. But after an introduction to meiosis, where they've had a chance to get the essential ideas, along with distinctions from mitosis, and the significance of meiosis, have them do this lab. Most students discover that their understanding of critical aspects of meiosis are often not as clear as they should be. This lab will show them the way!

The Worksheet is fairly self-explanatory.
1. Have the students read the Objective, Identification and Inventory, then ask them to report any chromosome sets with extra items or items missing.
2. Have them read the Assumptions. Emphasize that these are very important, and critical to success.
3. Have them read the Procedure, and commence doing it. They are to raise their hands when they think they've got their Mitosis sheet done correctly.
4. As they begin placing chromosomes on the Mitosis template, walk around quickly, looking for hands (where you should go as quickly as you can), and looking for proper progress (which you should confirm with "Good start", etc. If you see bad starts, say something like "Not quite... re-read Assumption #2" etc. You will find that you will get lots of exercise in this lab, moving through your entire array of desks many times.
5. See Teacher Directions for specific things to look for
6. As each student gets it right, over which you exclaim "She's got it!", that student proceeds to copy the layout on the separate Summary sheet, using the colored pencils (or shading in for blue chromosomes and leaving "pink" chromosomes open). As soon as the drawing is done, they are to put it UNDER their Worksheets (so neighbors can't just copy it easily) and proceed with the Meiosis phase.
7. Repeat #4-6 for the Meiosis phase.
8. When finished, and approved, student proceeds with #5 and 6. When class is done, students can begin parts F-H, and finish these for homework.

Next Day: Discussion
If you like, you could collect all worksheet/summary diagrams (back-to-back) for homework check, or have kids exchange them for in-class correction, or they can just keep them while you go around to stamp them if done, then go over the results in class. Use the Summary Key 1 on the overhead for the lab review, asking students to point out the critical distinctions. Point out where allowable variations can occur, and emphasize vertical continuity, so they recognize the flow, seeing each step as a frame in a film. Then have them look at the Summary Key 2 on the overhead, (for the homework assignment), and ask how many got it essentially correct (you should point out where there can be allowable variations). Let them ask questions about where they differed with the key; you may need to go out and take a look at some individual Summaries.

Ask students to submit what they wrote into Part F, 2-3 students per line, with discussion where needed.

Ask students for their responses to Part H. Guide their responses toward those in the key, as needed. Be sure they all realize that miTosis mainTains the chromosome number, and meiOsis LOwers the chromosome number from two sets to one set (2n--->n), and that this (in meiosis) is important for two reasons (see part H in the worksheet key).

Use the concepts as a basis for building questions on the critical distinctions and functions of mitosis and meiosis, and the essential reason why these two processes occur (much more important than memorizing the names of every stage).


When you teach the timing of mitosis (some time before doing this Mitosis & Meiosis lesson - although you could use it here and in many other lessons), consider using the technique for making critical elements of the Nature of Science (NoS) explicit and part of the material for students to learn. See details at Revising Instruction to Teach Nature of Science.


Some of the ideas in this lesson may have been adapted from earlier, unacknowledged sources without our knowledge. If the reader believes this to be the case, please let us know, and appropriate corrections will be made. Thanks.

1. Original Source: Larry Flammer, 1970

2. Edited / Revised for website by L. Flammer 9/2006


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