Wisconsin Fast Plants Network

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Here's a question we just received from a teacher in Ohio who is preparing to teach the AP biology selection investigation:

This will be my first year doing the AP Bio artificial selection lab and I just received my shipment of fast plant seeds. However, I am confused about one step in the lab and was wondering if you could help me understand.
The lab manual says, "As a class, pick a trait you want to try to affect. Find the top (or bottom) 10% of plants with that trait in the entire class’s population (e.g., out of a population of 150 plants, the 15 hairiest plants), and mark any that are in your plant bottle container. Using scissors, cut off the tops of the remaining plants in your container (those not in the top 10%)."
What constitutes the top of the plant? How far should my students cut?

The way the AP selection investigation (#1) is written was designed to set the stage for using the first population of Fast Plants for both the selection investigation and a Mendelian genetics inquiry. While this can be done and certainly is one way to get double-duty from your first Fast Plants population (and the time invested in growing them), actually isolating two distinct groups of breeding stocks from this first population and eliminating the possibility of inadvertent cross pollination can be logistically challenging--especially if this is your first experience with Fast Plants.

Alternatively (and particularly if this is your first year growing Fast Plants and/or facilitating AP Investigation #1 or any selection experiment) we recommend discarding, by snipping off at ground level, the 90% of the population that has lower levels of trait expression (for whatever trait you’ve selected). Then, you’re left with only the 10% you intend to intermate. This will be far easier to manage than trying to isolate the top 10% during pollination while still intermating (pollinating) the bottom 90% and keeping both groups’ seeds separate.

Once you’ve facilitated a selection experiment with students, reflect on your experience, and decide if you want to tackle running two breeding programs simultaneously next time--it is efficient use of plants and class time if you can do both well. We can talk more about various ways to accomplish effective isolation in another discussion if there is interest.

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