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Bean Toss (easy)

Bean Toss Game 

In this activity we will learn about the concepts of genetic bottlenecking and differential selection pressures. No worksheets are needed. It is helpful for students to have a sheet of paper, a pen, and calculators (one per group of students).

Teacher preparation: Buy a bag of mixed small beans or combine bags of beans to make a relatively homogeneous mix of at least 4 kinds of beans.

The set- up is to have students sit in groups at tables. If you don't have this option in your classroom, you can use the floor.

The scene:

Each table or group of students is an "island". They can give themselves a name. Let's pretend they are birds and if they eat the beans the beans will grow into new plants because they will be eaten by the bird and then will land somewhere along with the "droppings" that act as fertilizer (the way chili pepper seeds evolved to be distributed!). Each group should invent a hand shape or gesture that will allow them to pick up (not sweep up) the beans.

Pour about 100 beans on each table. Then give students 15 seconds to pick up the seeds using their bird technique. Yell, STOP! when time is up. Sweep up the remaining seeds from each table.

Have students drop the seeds they picked up on the table again. Walk to all the tables and make sure the seeds are spread out. Then announce students have another 15 seconds to pick up as many seeds as they can using their bird technique. Yell STOP! and repeat. After 4 iterations total (i.e. four generations), have students count the number of each kind of seed and divide it by the total number of seeds their group collected.

Obtain the proportion of each kind of seed for each island and write the data as a matrix on the board. Discuss what patterns were observed. Did allele frequency change? Which island had exerted the strongest selection pressure (i.e. which had the fewest remaining alleles or the highest percent of one bean/allele?)?  Discuss that even starting with the same kind of population, those subtle changes in bird technique were enough to steer evolution differently for populations on different islands. This is often how some varieties of crop are selected. The populations get bottlenecked for different alleles or features in different places.

Collect the beans for later use (you can grow them in the classroom!).