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Artificial Selection Lab
(University of California, Riverside)
(Bella Vista Middle School,
Variation and Natural Selection
PDF Copy of this Lesson, as Shown Here (9 Pages)
|Students are introduced to the field of experimental evolution by evaluating skeletal changes in mice that have been artificially selected over many generations for the behavioral trait of voluntary exercise wheel running. A video presentation by Dr. Theodore Garland, Jr. of the University of California, Riverside discusses the experimental design and presents the results of the collaborative research on the structural, metabolic, and neural changes in the selected lines of mice. In an inquiry-based activity, students develop hypotheses about the skeletal changes that might occur in the legs of the selected mouse populations and design an investigation using measurements taken from photographed femurs (thigh bones) of mice from both selected lines and non-selected control lines.|
|Experimental evolution allows the processes of evolution to be modeled and observed in the laboratory with real organisms.|
|1. A population of animals can be changed dramatically by
selective breeding over successive generations.
2. Selective breeding for a behavioral trait also causes changes in neurobiology, body structures (e.g., limb bones), metabolism, and biochemistry.
3. Variation in behavioral traits and any other associated biological traits can be passed on from parents to their offspring.
|1.Born to Run: Artificial Selection Lab Teacher Information.
2. Video of Dr. Theodore Garland, Jr. describing the artificial selection experiment
3. PowerPoint used by Dr. Garland in the video
4. Born to Run: Artificial Selection Lab Teacher PowerPoint to introduce the lab activity to your students
5. Born to Run: Artificial Selection Lab Student Handout
6. Femur digital photographs (JPG files) Zipped file for compact download
If using classroom computers, then all or some of these photos can be preloaded onto them.
If students use their own computers, then you can have the photos on one or more USB flash drives that the students pass around.
7. Computers with downloaded ImageJ freeware.
We suggest 1 computer per student or 1 per 2 students.
Printed copies of femur photographs, graph paper, and rulers
8. Optional: Excel files that contain the data on the body mass of each mouse, either without or with data on their femur lengths as measured by Dr. Garland and his collaborators.
|Four 45-minute periods, or equivalent:
A. Born to Run engage activity
B. Video presentation by Dr. Garland
C. Lab activity experimental design and data collection
D. Lesson summary and class discussion developing new hypotheses
Photographs of mouse femurs, either digital or printed (see above under MATERIALS).
This lesson is best used as a culminating activity that links the concepts learned during the study of evolution with the skills outlined in the investigation and inquiry standards.
Required prior knowledge
Using the data sets
Each image is labeled with the following convention C/S for control or selected; individual identification number; LF/RF for Left or Right femur; f/m for male or female; and a number representing the line of control (designated as lines 1, 2, 4 or 5) or selected (designated as lines 3, 6, 7 or 8) mouse. Body mass for each individual is contained in an Excel file (see MATERIALS) and can be further used to evaluate the collected data (e.g., larger-bodied mice would be expected to have larger limb bones, all else being equal).
Images of other bones (e.g., pelvis, scapula) may be available by contacting Dr. Garland [office phone 951-827-3524; firstname.lastname@example.org].
Supplemental Information for Teachers
It is important to understand that the experiment includes
4 separate selectively bred High Runner lines and 4 additional
non-selected control lines of mice. This sort of replication
is required in any scientific experiment. Here, it is necessary
to allow strong inferences concerning what traits have really
evolved as correlated responses to breeding for high voluntary
wheel running. However, for purposes of your exercises, you
may wish to skip over some of this detail in the explanation
of the experiment and/or with respect to which bones students
ENGAGE: Evaluating prior knowledge and introducing the artificial selection experiment:
Preparation: Download and make copies of Artificial Selection Lab Student Handout. Download and review the Teacher PowerPoint file you will use to introduce this exercise to your students. Download Dr. Garland's video presentation. Download the PowerPoint presentation that Dr. Garland used in the video (this may be helpful for answering any questions students have after watching the video).
Presentation: Distribute Artificial Selection Lab Student Handout. Students draw a real or hypothetical organism that is a good runner. Have groups compare their drawings and share the commonalities. Record student responses on the board.
Evaluate student's prior knowledge of evolutionary processes and outcomes, including adaptations by including such questions as: "How does this feature adapt the organism to run fast?" "How might natural selection act on a population of organisms that lacks this adaptation?" You can push student's thinking by sketching stick figures if students mention long legs, draw a stick figure with one long and one short leg. Ask "How might the length of this organism's leg impact its ability to run? Are there other factors that might be important?"
Ask students to write a paragraph to answer: "Explain how natural selection might act on a population of organisms that lacks this adaptation." Collect the papers to evaluate the student's prior knowledge. Use the student responses to identify misconceptions that need to be clarified or concepts that require additional instruction/clarification.
EXPLORE A: Learning about experimental approaches to studying evolution:
Presentation: Explain that you will be showing a video of a research scientist who studies experimental evolution.
In his experiment, he has modeled natural selection in the laboratory.
EXPLORE B: Using Inquiry to study the effect of artificial selection on leg bones of mice: Developing a hypothesis, designing the method and performing the measurements:
Preparation: See Materials and Teaching
Strategy above Measurement Techniques and
Using The Data Sets.
Presentation: Distribute the Artificial Selection Lab Student Handout and show the Teacher PowerPoint, which summarizes the steps of the experimental design process. Alternatively, you can also display the Artificial Selection Lab handout using a projector to display the images on the teacher's computer and discuss each step.
Ask students to discuss "What would you expect to be true about the legs of a good runner?" Have students discuss with their lab group. Have representatives of each group share the ideas with the class. [Students will generally mention leg length, muscles, and body size]. Prompt students to recall Dr. Garland's video presentation and ask them to discuss "Would the leg bones of mice bred for voluntary wheel running also show changes? What kind of changes might you expect?"
It is helpful to give groups of students actual femurs
of mice so that they can visualize what the bones look like.
A good source of mouse femurs is to dissect them out of owl
pellets, which are quite inexpensive or are often already available
at many school sites. Students become aware that the bones are
actually tiny and that the photographs you will show later significantly
magnifies the actual bones. Scientists in Dr. Garland's lab
have already performed measurements on these bones using micrometers.
Showing an actual micrometer at this point drives home the point
of how difficult the technique actually is. If you don't have
a micrometer readily available, Google Images is a good source
of images. For example, an animated micrometer is shown on
Show students the femur pictures and explain that they are photographs of leg bones of both selected and control mice.
Developing a hypothesis: Prompt students to discuss the things which might be different in the legs of selected and control animals, and list them in part A of their lab handout. Students must then decide what they will measure on the femur pictures and record it in Part B of their lab handout. If students are working in groups, the decision must be made collaboratively. [Occasionally students will list changes in Part A which cannot be determined using the available samples. Remind them that they need to be able to measure something to be able to test this.] Then have students record their hypothesis. The if-then format is not encouraged. Just be sure that it provides a tentative explanation that can be tested, or describes a possible interaction that can be tested.
Developing a Method: Tell students to decide how they will be measuring the bones. Demonstrate measuring femoral length in different images using different landmark points. Ask if this would be a good way to collect data. What is wrong with it? How could you improve it?? Students will readily correct this technique. On their lab handout, have them indicate how they will measure the samples by drawing a line on the image.
Performing the measurements: Students can measure
the samples in two different variations: automated, using Image
J freeware and manual using direct measurement of images.
Procedure for automated measurements: Refer students to the instructions for using Image J on their handout. Guide students through the steps. Demonstrate the technique on the teacher computer using a projector. Remind students to select summarize to display average measurements after finishing to display the averages. Image J files are saved as Excel files, so it is easy if you and your students choose to save the data for later analysis in math or computer classes. (See extensions and variations cross-curricular options below.) Cautionary note: Students will not be able to use this feature if they measure both control and selected data sets together. The summarize feature averages all the samples in the data set.
Preparation for manual measurements: Print images (four per page works well). The images can be laminated for repeated use. Mark the back of each image so students can distinguish selected and control samples, as well as individual mice. Prepare a folder for each lab group containing images from selected and control animals. Have metric rulers and calculators available.
Procedure for manual measurements: Distribute manila folders containing a selection of printed images from both selected and control animals. Students can successfully measure 8 images each and then compile their results with those of three other students in their lab group. You can adjust this as necessary; however, it is unrealistic to assume that all the available photographs can be measured. If all the students have measured the same features (for example, femoral length), then the class data can be compiled.
Optional math extension for manual measurements: (see
Extension section) Remind students that the measurements they
have made do not represent actual lengths of the femurs. Compare
an actual mouse femur with the image, either on an overhead projector
or a doc cam. Ask students how they might use the measurement
they made to calculate the actual size of the bone. Offer an
extra credit option for students to calculate the actual sizes
of the femurs. Ask students to defend the validity of using
values that are not corrected for magnification in forming their
EXPLAIN: Presenting the data and writing a conclusion.
Results and Conclusion: Ask: What would be the best way to graph these results? [Students may quickly respond with "bar graph" if students are struggling ask: Name some different kinds of graphs. Which would be the best kind to use to show the results from this investigation?] Use the Artificial Selection Lab Teacher PowerPoint to describe the required elements. Student groups graph their results on poster paper, white boards or overhead transparencies and share the results with the rest of the class. Frequently, multiple groups will measure leg length and get different results for selected and control groups. Lead discussions where the class analyzes why these differences might occur (e.g., sampling error).
Ask students to brainstorm what things would belong in a good conclusion. Gather the student answers and list them on a poster paper. Edit the list as a class and post it in the classroom for student reference as they write their conclusion piece. Alternative option: Review the Artificial Selection Lab Teacher PowerPoint panel describing the required elements for the conclusion.
Students lab reports serve as the summative assessment for this activity. A rubric for evaluating the lab reports and conclusion is included in Artificial Selection Lab Teacher Information
Data Analysis Extensions:
Images of right and left femora of selected and control specimens
from two different generations of mice are available for students
to measure. Class discussions that take place immediately following
Dr. Garland's video might generate a variety of questions that
could easily be evaluated by rearranging the images in the folders.
1) Sex differences by comparing male and female selected and control
2) Differences in leg symmetry by comparing left and right bones of selected and control mice
3) Differences in generations by comparing selected and control in two generations
Remind students that each of the specimens measured come from
different mice, which have different body sizes. Can any differences
be attributed to difference in body size? How might students
correct for this? The body mass at death for each of the specimens
is available in an Excel file (Listing_for_STEM_April_2012_without_Femur_Data.xls). Another version of this file includes the data for right and left femur lengths in mm, as used in the publication by Garland and Freeman (2005)
(Listing_for_STEM_April_2012_with_Femur_Data.xls). Students can make graphs of femur length (Y axis) versus body mass (X axis).
Some pre-planning with math and computer teachers might allow for students to integrate the graphing and data analysis portions of this lab into their other classes. Alternatively, you can address as many or as few of these issues while doing the lesson, depending on available time.
Graphing: Which is the best type of graph to display the data? Often students have difficulty choosing between the different types of graphs. Does the scale you chose show a true representation of the data or is it misleading?
Statistics: Is a difference significant? Often students think that any two numbers that are not identical represent an important difference. They are not aware that measurements are subject to error (e.g., human error, differences in image magnification, insufficient sample numbers).
Ratio and proportion: Manual measurement of printouts of the images yields measurements that are not corrected for magnification and will impact the results when differences are small. The scale bar in each picture allows students to use simple proportions to calculate actual sizes of the bones, and provides a math connection. In fact, there are slight differences in the magnification of each image. Have students measure the scale bar in successive images to see this for themselves. Ask how they might correct for this factor.
Computer use: Saving the data collected in Image J in Excel allows students to use the graphing features to generate and manipulate graphs to display differences. Using the function bar allows students to calculate averages, standard deviation, etc. Similar things can be done with the free spreadsheet on Google Drive.
NGSS: Next Generation Science Standards (2013): (Second Draft) Under Development:
California Science Education Standards (2003):
National Science Education Standards (1995)
SCIENCE AS INQUIRY: Ability to do scientific inquiry; Understandings about scientific inquiry
SCIENCE AND TECHNOLOGY: Abilities of technological design; Understandings about science and technology
CONTENT: Grades 5-8
Some of the ideas in this lesson may have been adapted from earlier, unacknowledged sources without our knowledge. If the reader believes this to be the case, please let us know, and appropriate corrections will be made. Thanks.
1. Original Source: Theodore Garland, Jr., Ph.D.
2. Minor editing to ENSIweb Format by: Larry Flammer
3. Reviewed by: Martin Nickels, Craig Nelson, Jean Beard: Jan. 2013
|CREDITS||This work was supported by an NSF grant IOS-1121273 (Garland) and by an American Physiological Society Frontiers fellowship (Radojcic), with assistance from Dr. Heidi Schutz and the University of California, Riverside.|