High School Biology: Fast Plant Genetics

Yesterday I taught a high school genetics lesson using Fast Plants as the study organism.  It was the first day of class for my “relaxed” homeschool biology class.  (I also have a “serious” homeschool biology class which is filled with students who have considerably more experience with science and greater interest in rigor.)

I started the lesson by proposing two different possibilities for the way traits might be passed from one generation to the next: Are genes discrete (as modeled by the pompoms) or do they mix (as modeled by the colored water)?

fast plants 4
This is the visual model I used to help students think about the implications of having genetic traits that stayed discrete vs. genetic traits that mixed.

The next step was for students to observe the colors of seedlings (either green or purple) from P1, P2, F1, and F2 generations and try to formulate ideas about how inheritance works.  (Actually these seedlings were a dihybrid cross, with color and “hairiness” of the plants as the two traits.  However, my initial evaluation of the class suggested that they would be sufficiently challenged by investigating a monohybrid cross, so we limited our attention to plant color.)

fast plants 5
Here, the seedlings are all mixed up. But in the class the petri dishes of P1, P2, F1, and F2 seedlings were carefully organized.

It wasn’t easy – although this is a high school class, most of the students have had very little exposure to science.  In some cases, this is actually their first formal exposure to science.  Fortunately, two of the students took my middle school biology class last year and a third has taken a variety of science classes taught by other teacher.  Those three students were able to model making and testing hypotheses for the other students.

fast plants 3
Working together to make observations and trying to figure out what the observations mean.

Eventually the students, with some prompting in the form of leading questions, came to a consensus that biological inheritance follows the “pompom” model rather than the “colored water” model.  Their evidence for this was that the green color of the P1 parent plants was entirely hidden by the purple color of the P2 parents in the F1 generation.  However, the green color re-surfaced in some of the F2 generation, providing evidence that it didn’t actually go away (or even get diluted).  Some students were able to explain themselves well and convinced me that they understood the concept.  Others were visibly struggling and clearly had not fully understood.  All of the students need practice with basic genetics vocabulary and problem solving.

On the whole, I’d say this lesson was a success, despite the fact that most of the students did not master the material the way I want them to.  There were simply too many things going on – not only was there a tremendous amount of new science content and vocabulary but there were new expectations about using observation to support or reject a hypothesis. We will revisit Mendelian genetics and scientific inquiry several more times over the next few classes.  Study organisms will include humans (with a lab about the genetics of taste), fruit flies (in a paper lab, since we can not have live flies in our work space), and fantasy creatures that the students will invent.  Given the progress I saw in our first class, I am optimistic that the students will achieve a good level of knowledge about genetics with repeated exposure.


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