A Mini-Lesson

MITOSIS & MEIOSIS:
Doing it on the Table

Larry Flammer

Click Here for PDF copy of this Lesson

GENETICS

 SYNOPSIS

 CONCEPTS

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).

 MATERIALS

 STUDENT HANDOUTS

 TEACHING STRATEGY

See Teacher Directions for details
Preparation:
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.

Context
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!

Presentation
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).

Assessment
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).

 ATTRIBUTION

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