Turkeys in the Cell --
The Meiosis Square Dance
1991 Woodrow Wilson Biology Institute
- identify synapsis as the key event in meiosis and explain how synapsis leads to the formation of haploid gametes.
- understand the differences between the processes of mitosis and meiosis.
- explain how meiosis generates new combinations for natural selection.
The visualization of 4-dimensional events is difficult with two-dimensional illustrations. Processes like mitosis and meiosis, photosynthesis and protein synthesis can be understood more readily if the events can be displayed in some memorable way in real time. One way is to choreograph such events as dances.
The key differences between mitosis and meiosis is something students frequently stumble over. Here is a dance to help them grasp the significance of synapsis. Charlotte Auerbach had referred to mitosis and meiosis as the "dance of the chromosomes," What kind of dance might they do? It seemed clear (?!) that they would do a square dance, and that made possible a good illustration of synapsis.
Meiosis is a very important process in biology. It is at the root of sexual reproduction, making possible the generation of haploid gametes from diploid cells. The production of new combinations of genes at each generation seems to be an essential advantage of sexual reproduction since it makes possible far more possibilities for natural selection to act on than can be possible if mutation occurs in asexual orgnaisms. Adaptation to changing environments, whether for humans or any other sexually reproducing organism, can happen more readily if there are more combinations to choose from. So meiosis is not just a process people have to memorize, but one of the driving forces in our interaction with the environment.
- Bandanas. You will need 4 bandanas of the same color for each chromosome pair you want to use in the square dance. I use 3 chromosomes, so I use 4 red,4 blue and 4 brown bandanas.
- A tape of square dance music. Use only instrumental music without singing or other voice performance. Turkey in the straw is nice, but not essential. I recorded my music from a Wait Disney Album of the Bear Country Jamboree.
- Students to do the square dance. You will need 4 students for each chromosome pair, one human to dance the part of each chromatid. If you have students of each sex in your class, use two males and two females for each chromosome pair to symbolize the maternal and paternal chromosomes.
- An illustration of the structure of a chromosome and a diagram of meiosis. You can develop these on a board, use an overhead or have slides.
- It is best to cover mitosis first and then meiosis. After mitosis has been covered, point out that meiosis resembles mitosis in many ways. Much of the same terminology is used for the events of division, but there are two dramatic differences:
- There are two divisions instead of one.
- The chromosomes line up separately on the spindle for metaphase of mitosis, but at the first division of meiosis the chromosomes pair in a process called synapsis. In synapsis, homologous chromosomes pair tightly along their length and then move to opposite poles so that only one of each pair of chromosomes ends up in each cell after the first division.
- It is best if you develop a diagram on the board or screen that students can refer to during the dance. Be sure they get a chance to ask questions before you dance, since that will make some of the issues more vivid in their minds as they learn the dance.
- Recruit your dancers. Indicate that you will be showing them the dance of the chromosomes to illustrate an important point about meiosis.
- Go through the dance once step by step, indicating what the dancers should do, what square dance calls you will make, and how the steps relate to the meiosis diagram you developed on the board.
- Be sure the dancers are comfortable with the steps. Then turn on the music and begin the actual dance. Act as caller during the dance, and encourage the students who are not dancing to clap along to the music so it has a good square dance feel.
- When the dance is over and everyone has settled down, review the steps of meiosis that are on the board. This repetition of the explanation in several different forms is important.
- One symbol = one student (e.g. K or U or m), and therefore a chromatid.
- A pair of symbols = 2 students with linked arms (e.g.mm or KK) who are therefore a chromosome with two chromatids.
These are homologous pairs:
- KK are red bandanas
- mmare blue bandanas
- UU are brown bandanas
- Early prophase of first meiosis. Each chromosome has 2 chromatids. But they are not yet synapsed and are arranged at random in the nucleus. Square dance call: "Everyone move around at random. Move at random."
- Late prophase of first meiosis. The homologous chromosomes now find each other by some unknown process and pair. This pairing of homologous chromosomes is called synapsis. Square dance call: "Everyone synapse. All synapse."
- Metaphase of first meiosis. Now the synapsed chromosomes move to the metaphase plate. They line up there, but their orientation with respect to maternal and paternal chromosomes is fully at random. Square dance call: "Mosey on down to the metaphase plate. All metaphase."
- Anaphase of first meiosis The chromsomes go to the poles. At this point note that entire chromosomes with two chromatids are going to each pole. The result of this movement is that each pole receives a complete haploid set of chromosomes. This is the inevitable consequence of synapsis. This is the function of synapsis. Square dance call: "Now anaphase your homolog. All anaphase."
- Telophase of first meiosis and telophase of second meiosis. These phases grade into each other and are not distinguishable for all organisms. So I just deal with them together as a convenient transition to the second division. The chromosomes are now at the poles in separate nuclei ready for a second division. Square dance call: "Now telophase and you're in prophase again. Second prophase."
- Metaphase of second meiosis Again the chromosomes line up on their metaphase plates, but this time they have no homologue to synapse with. There is no synapsis in the second meiotic division. Square dance call: "Mosey on down to the metaphase plate. Second metaphase."
- Anaphase of second meiosis. This time the chromosomes separate into chromatids, and the chromatids go to the poles. But this time the number of chromosomes going to each pole is the haploid number. It's just the chromatids per chromosome that has changed. Square dance call: "Now anaphase your partner. All anaphase."
- Telophase of second meiosis. We now have four cells, each with a complete haploid set of chromosomes. The dance is over.