This let the students build their own understanding of how the alleles (versions of genes) an individual has are passed into the gametes they produce. Having this process clear is essential for our next step, understanding how the alleles of the two parents determine the genetic properties of their offspring.
The problems we did were designed to take us through increasingly complex situations. The complexities arise from several factors. We began by considering alleles of a single gene, then moved to alleles of two different genes. We also began by considering the results of a single meiosis, which I could demonstrate by labeling and moving around transparent coloured strips on the overhead projector, and then moved to considering the pooled results of the many meioses that produce, for example, sperm. With two genes we also had to take into account whether they were located on different chromosomes or on the same chromosome, and, if the latter, whether there could be a crossover between them.
I wanted students to work through these problems using paper strips as model chromosomes (they can write the allele names on the strips, move the trips through meiosis, and then look at which alleles end up in which gametes). Some students did this, and the expressions on their faces showed the discoveries they were making. But many students clearly felt that working with model chromosomes was unnecessary, and that they could solve the problems either by just thinking about them or by drawing chromosomes in their notebooks. Sadly, repeatedly getting the wrong answer didn't seem to change this attitude.
I thought these were very simple problems, and yet most students initially got them wrong. This is where the clicker technology really reveals its value. I think I now need to figure out how to tabulate the students' answers so I can share them with other instructors of this course. I think they may also not realize how difficult these concepts are for students.
Although we didn't actually deal with a situation where a crossover did happen, I would like students to be able to deal with this, at least at the level of a single meiosis. But we'd have to spend at least a bit of class time on it. Maybe I could demo it with the transparent strips, and then give it as a clicker question for the next class.