Mitosis Models With Pipe Cleaners

Ok. My prepared slides of mitosis are missing, so I had to scramble to find an activity to do on the subject with my classes. I remembered seeing some students from years past doing models of mitosis with pipe cleaners to represent (obviously) the chromosomes.

Now, I had thought this was a pretty lame activity - look at the pictures in the book, reproduce the stages of mitosis (P-M-A-T) with pieces of pipe cleaner and move on. Nonetheless, I needed some kind of activity and I didn't have much time to look for something else. So I threw together the materials and headed to class. Explained the procedure. Showed students the pictures in the book (we had already discussed the cell cycle & stages of mitosis, read the chapter & answered questions, etc), made a few suggestions like only using one or at most a pair of chromosomes, identical colors for sister chromatids, different color for the homologs, etc.

I was wrong about the lame thing. They really struggled. Because they weren't just copying the pictures in the books, they had to think about the process and sort out how the chromosomes separated and figure out how to model that with real materials. Early on, some students were using different colors for the "sisters" (I don't care if they know the term chromatids at this point. So I let them just shorten it to sisters. Having told them this, they proceeded to use the term sister chromatids anyway!). Others were using the same colors for both chromosomes in a homologous pair. Some of their models ended up with daughter cells having pairs of sister chromatids rather than a homologous pair. I got questions like, "How long should the spindles be?" All these issues had to be sorted out. The funny thing is, they had no trouble answering questions from our discussion & the textbook that could be answered by simply memorizing information about the process - "What happens in metaphase?" e.g.) But those were just words. They didn't actually have a mental model yet of the process.

A more disturbing problem (for me looking at it from a pedagogical standpoint) was a sort of intellectual laziness, for lack of a better term. I had given them the option of using one chromosome or a pair of chromosomes in their models, and emphasized repeatedly that we were making a very simplified model, and that different organisms have any number of possible chromosome numbers, and whatever happened in our model to a single chromosome, happens in the real world to all the chromosomes in a cell. We have mostly talked about humans and our 46, but some organisms have only 2 chromosomes, others over a hundred. (Bacteria have a single chromosome, but they don't divide by mitosis). The problem came when I illustrated metaphase on the whiteboard using 3 chromosomes - just to use a different number from theirs. Afterward I walked around, and several students had placed - you guessed it - three chromosomes in their metaphase, even though they only had one or 2 chromosomes in their prophase! They were looking for someone to just tell them what to do without investing any more thought than absolutely necessary. I might not be so critical if they had at least asked questions about it before making the mistake, but they didn't.

I can see two important things happening in this process. First, they are clarifying their thinking about a fundamental process - and it's good that I see the difficulty now rather than later when we move on to meiosis. Secondly, they are learning how to make models - a skill in itself. The whole concept that in a model we often need some way of indicating that two things are either the same (sister chromatids) or different (homologous pairs) was apparently a new idea for some students.

I highly recommend this or a similar activity for students learning mitosis & meiosis. If I have time, I will do a more formal write-up with lab sheets and post it all later.