To start this lesson, I ask for the genetic drift experts from the How does evolution happen? jigsaw activity to remind tables of the meaning of genetic drift. I then present the Founder Effect, Bottle Necking, and Genetic Drift video that does a great job of explaining the founder effect and bottlenecking - make sure to watch out for the special effect at 1:33.
After the video, I ask students to bring out any device they have and go to the padlet wall I created beforehand. I tell the students to post one idea about the meaning of these two concepts. It is important that these two concepts remain displayed throughout the lab since students will need to refer back to them during the lab.
Note to teachers: In the discussion that I have to clarify any lingering doubts that arise from the video I often use a "classroom story" as an example. I choose a couple of table groups as the only survivors of a classroom disaster, and we imagine what the population of our classroom would look like of only these students survive (bottleneck). In this year's example I chose tables that had only two asian girls and no blondes at all. This is why in the picture of the padlet you see the idea "No blondes, only Asians". I invite you to read my reflection to see how this strategy improves engagement and joy in the classroom.
I tell the students that we will continue to work with the Colored candius organisms. I ask the students to pick up their bags of candy and Lab Sheet.
This time, each table will get one full-sized bag. Each student will then blindly obtain a genetic drift population of 6 candies and determine its frequency (SP5). After each student has calculated the frequency of each color in their "personal" genetic drift population, the table counts and determines the frequency of each color in the original population (number of candies in the complete bag). This is what the results could look like:
Once students have their data, it is time to analyze and interpret it (SP4). Even though the students will work independently, I still encourage them to talk to each other and share their ideas since this is where much of the clarification (examine understanding in light of the evidence) and engaging in argument from data centered evidence (SP7) happens. This simple lab also serves as a model for the students to help explain cause and effect relationships and predict how gene frequency may be affected by the founder or bottleneck effects of genetic drift (SP2, CCC Cause and Effect).
As students finish answering the questions in their lab sheet, I ask that they turn them in. As I look at them I am paying particular attention to their responses to questions 4 and 7 which reveal their understanding of the effects of genetic drift. In question 4, students arrive at the realization that in a genetic drift population the allele frequencies may never match those of the original population. As simply stated by one of the students, "The colors will never be equal since I already lost all the brown and orange in the first group." In question 7, students come up with scenarios that could cause the genetic drift they observed, and identify their imagined scenario as founder effect or bottleneck. This question allows students to develop their ideas about one of the concepts a little bit further (SW1, SW2, SW3, SW4).
Watch as the students move through the lab and achieve understanding.
To close this lesson, I ask for student volunteers to share their causes for genetic drift with the class. Willing volunteers tend to offer up funny and far-fetched scenarios, and although they might not provide all the concept information I would wish when done verbally, they provide for a way to encourage joy in my classroom.