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MUSE | Natural Selection | Unit Overview and Materials | Section 3: Using Darwin's Model... | 3B: Exploring Variation and Heritability | Handout #1


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Handout #1: Evolution by Artificial Selection in Wisconsin Fast Plants™

In this section of the course, you will be working with data from a series of artificial selection experiments on Wisconsin Fast Plants. The data you will study were collected by college students. Bruce Fall, at the University of Minnesota, compiled the data and provided it to us for the activities you will be doing in the next few days.

In any case of artificial selection, the experimenter or breeder selects certain traits that are to be increased or exaggerated in later generations. You have already seen examples of this in pigeon and dog breeding. In this Fast Plant case, the trait of interest is the number of trichomes (plant hairs) on the petiole (stem) of the first true leaf of the fast plant. This very specific definition is necessary because it allows you to measure an informative trait within a reasonable amount of time. You could count the trichomes on the whole plant as it grows, but that would take too long! A detailed definition also clarifies how the trait will be counted or measured, so that valid comparisons of results can be made later.

1. Make observations of the trichomes on Fast Plants that are growing in your classroom. You will need to use magnifiers or a dissecting microscope to see and count these small structures. Describe the trichomes.

2. Count the number of trichomes on the petiole (stem) of the first true leaf on one plant and write that number below. Find another plant and count the same trait on that plant. Were they the same?

3. Identify several other traits that vary within the Fast Plant population in your classroom. In what ways do they vary? Describe at least two traits below. For example, not every plant flowers at the exact same moment so we could say that the timing varies between plants. Another example might be the space between two structures on the plant. That kind of variation could be measured in centimeters.

4. Identify several traits that do not seem to vary within the Fast Plant population in your classroom.

5. Was it more difficult to find traits that vary or traits that don't vary? Why do you think this is so?


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