Biology Lab: Artificial Selection

Preparation for Lab

Concept: Interbreeding individuals with desired characteristics can increase the frequency of occurence in the general population over several generations. This process of selective breeding accomplishes the same results as natural selection, but since it involves a human-directed purpose, it is considered artificial.

Alternative Lab

There is no artificial selection or selective breeding experiment in The Illustrated Guide to Home Biology Experiments.

The following lab requires you to download software from the National Institute for Health. Please check with your parents before installing any software on your computer.

The following exercise allows you to perform analysis on data collected by another researcher. This is sometimes called "dry-labbing" your data, but in large institutions, it is highly likely that the senior researcher will have assistants actually perform the experiment, making all measurements required, and then perform his analysis on the data they have collected.

For this experiment, Dr. Garland has already bred mice through fifty generations, with each individual to be bred selected for their running capacity, or as part of a random control group. "Running capacity" was measured by the speed of the runner (number of revolutions per minute) rather than by length of time running.

Goal: To determine whether selective breeding increases running capacity in mice.

Procedure

1. Review the experimental design and purpose by watching the YouTube video of Dr. Garland, who conducted the actual experiment.
2. The slides for Dr. Garland's presentation are available at the Slideplayer site.
3. Read through Dr. Radojcic's description of the lab work and methodology.
4. Print off the student worksheet.
5. Download the appropriate ImageJ application (select based on your computer operating system) from the NIH ImageJ Application site, and follow the instructions to install the correct version on your computer.
6. Review the instructions for using the program on this short instruction PDF ImageJ Basics. Using the Open Samples option, select the "Blobs" picture, allow it to open, and then use each of the tools to a draw line fron one side of a blob to the other. Information about the line, including its length, will display on the toolbar. Measure the diameter of several blobs. Then use one of the area selection tools to surround a blob and determine its area (value). Play with the other tool features so that you can use them on the data pictures.

   Note: If you are not able to download the ImageJ viewer, which allows you to measure distances on the computer screen image display, you can still collect measurement data by printing your selected pictures and using a meter stick graduated in millimeters to measure the printed image.

7. The images you need are at UC Berkely in the G12_Split_for_STEM folder. This contains a collection of femora images. Each folder contains pictures of the right femur (RF) and left femur (LF) for a particular mouse. For example, "C14001"LF" is the picture of the left femur of control mouse #14001. The following images should be available (the pictures are numbered below for easy identification):

   G12_Control_Female_Femora folder

   1. G12_Control_L1_Female_Femora
   2. G12_Control_L2_Female_Femora
   3. G12_Control_L4_Female_Femora
   4. G12_Control_L5_Female_Femora

      G12_Control_Male_Femora Folder

   5. G12_Control_L1_Male_Femora
   6. G12_Control_L2_Male_Femora
   7. G12_Control_L4_Male_Femora
   8. G12_Control_L5_Male_Femora

      G12_Selected_Female_Femora folder

   9. G12_Selected_L3_Female_Femora
   10. G12_Selected_L6_Female_Femora
   11. G12_Selected_L7_Female_Femora
   12. G12_Selected_L8_Female_Femora

       G12_Selected_Male_Femora folder

   13. G12_Selected_L3_Male_Femora
   14. G12_Selected_L6_Male_Femora
   15. G12_Selected_L7_Male_Femora
   16. G12_Selected_L8_Male_Femora

   Decide whether you want to study male or female femora. If you chose females, for example, you should now go to the G12_Control_Female_Femora folder and select one of the subfolders. Inside the folder will be pairs of photos of the left and right femurs of each female control mouse in that group. Download 10 pairs of femur photographs. If there are not enough pairs in the folder you chose, use another control folder for that gender and download pairs of photos until you have 10 pairs. Then do the same thing with the selected mice (those bred to run). You should have 20 control photographs, a left and a right photo for each of 10 control mice, and 20 selected photos, a left and a right photo for each of 10 selected mice, all of the same gender.

8. Lab Notebook Preparation: In your lab report:
   • Make a list of characteristics that might identify a "good runner". Compare your list with those of your classmates and add characteristics you missed.
   • Identify traits that might be affected by natural selection, and explain how these traits may shift under appropriate conditions. What leg adaptations might evolve (i.e., increase or decrease in frequency in the population)? Identify one characteristic to study.
   • You will be viewing leg femurs (upper leg bone) segments of mice over several generations. Formulate your chief question: Are the femurs of mice selectively bred for wheel running _____________?
   • What will you measure on the femur to answer your question?
   • Formulate a hypotheses: If _______ (some condition exists), then ______ (result). Explain why you expect the result you chose.
9. Measurements:
   Using the ImageJ application, follow this procedure to measure bone lengths for the control female femurs:
   1. File – open: Select image
      • Select line tool on the tool bar
      • Draw line on the ruler that is 15 mm long (1.5 cm)
   2. Analyze – set scale
      • Enter 15 in “Known scale” and mm in “Unit of length”. You can choose to
      • display in mm also and set the number of decimals of accuracy.
      • Click “Global” This will apply the scale measurement to each picture that you measure thereafter.
      • Draw a line at the dimension which will be measured. The scale bar will display the measurement as well as the angle of the line. This will disappear when you click the end point of the line.
   3. Analyze-measure: A data table will appear with the first measurement
   4. File – open next : The next image to be measured appears
      • Draw a new line on the new femur picture.
   5. Analyze – measure: The next length will be displayed on the data table
   6. When your measurements are complete, select Analyze – summarize.
   7. Record the average from the displayed information. You will be graphing these data later.
   
   Repeat the steps above for the control male femurs, and the two sets of selected specimen femurs.
10. Record your data in an appropriate data table, e.g., in a spreadsheet with columns that allow you to compare selected specimens with the equivalent control specimens. Create averages for each group of measurements.
11. Analysis:
    • Are there trends in your data? Can you make conclusions about the effect of selecting for the trait of wheel running on the selected mice? How does this effect compare with the same trait on the control mice?
    • How do the average measurements support your conclusions?
    • Do your analysis and your conclusions support or contradict your hypothesis?
    • What steps in your analysis might have contributed to errors or inaccuracies?
    • Explain any other observations and inferences you might make from them.

Post your formal report to the Moodle.

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