Litter Sizes in Two Strains of Inbred Mice

Transcription

1 Lab 0 Litter Sizes in Two Strains of Inbred Mice Introduction To do this lab you will be using four software packages: 1. Mouse Models. A set of mouse behavioral development models written by Jeff Schank. 2. Microsoft Excel. A spreadsheet program that allows you to rearrange, manipulate and graph data (it also has limited statistical analysis capabilities). 3. Microsoft Word. A word processing program that will allow you to combine text with tables and graphics. 4. Statistica. A statistical analysis package, which allows you to do very sophisticated statistical analyses with your data. In all of the simulation labs you will be doing, you are to suppose that you are working with two inbred strains of mice (inbred strains are produced by brother-sister matings over many generations to produce essentially genetically identical mice). The two inbred strains you will be mating are BALB (a white furred mouse) and C57 (a black furred mouse). The question you are interested in investigating today is whether these two strains of inbred mice have different average litter sizes. There are two possible answers as the problem has been posed: either they have the same litter size or they don't. Your hypothesis is that there is a strain difference in average litter size. Therefore, your null hypothesis is: H 0 : There is no difference in mean litter size between strains. Breeding mice takes up time, space and resources, so you cannot breed too many. You decide that a reasonable number is to breed 10 BALB females and 10 C57 females. Lab Setup Step 1: Create a lab group folder in the PSC113 folder within your lab section folder (Figure 1 illustrates where our PSC113 lab folder is located). Once you open your lab section folder, it should look something like Figure 2. You will need to come up with a unique name for your lab group. Don t make it simple because you will be sharing this space with others, and we can t have two folders with the same name. Figure 3 illustrates an example lab folder. Step 2: Copy the contents of the folder class files and paste them into the new folder you created. 1

2 Figure 1. The labs are located in the Young 162 Share drive, circled in red. Figure 2. Inside your lab-section folder. 2

3 Figure 3. A new folder is created with the name LabGroup-JKM. Step 3: Run a simulated experiment. Double click Run Mouse Models. Choose the Model tab in the control window. Simulate 10 litters per treatment. Use Model 0 and check savedatatofile (see Figure 4 and Figure 5). Figure 4. Mouse simulations control window. Select Model 0 from the Model tab (circled in red) and check savedatatofile to save your data to a text file you can open with Excel. 3

4 Figure 5. Mouse simulations simulation window. Step 4: After you have run your simulation and saved the data (the latter is not automatic), a new folder, illustrated in Figure 6, is created that contains your data. Open the data in Excel and save it in an Excel workbook as illustrated in Figures 7 through 10. Figure 6. Once you have navigated the Excel open dialog window to your folder, you will see a new data folder created with the name datamodel0. 4

5 Figure 7. Data file in the folder you just entered, open this file in Excel. Figure 8. The text file dialog box that appears in Excel, click Finish circled in red. 5

6 Figure 9. The save dialog box in Excel. Save as Excel Workbook, circled in red. Step 5: Now you are ready to analyze your data. Open up Statistica, and then open up the workbook you just saved as illustrated in Figures 10 and 11. Then analyze the data with an independent t-test by following the instructions in Figures 12 to 16. Figure 10. Statistica open dialog box. Select the Excel file circled in red. 6

7 Figure 11. Statistica dialog box that appears after you have selected the file to open in Figure 10. Select Open as an Excel Workbook circled in red. Figure 12. Data setup in Statistica. Make sure the first data column is B as circled in red. Figure 13. Data type setup. Click OK. 7

8 Figure 14. The dialog window that appears when you select Basic Statistics and Tables from the Statistics menu. Select t-test, independent by variable and click OK. Figure 15. The variable assignment dialog box. Select a different one for the first and second variables and click OK. 8

9 Figure 15. Click on Summary, circled in red, to get your analysis. Figure 16. Your results should look similar to those illustrated here but not identical to these. 9

10 Step 6: Mini-Lab Report. Create a word file and paste in your results table illustrated in Figure 16. Explain what you think it means. To do this, answer the following questions: (1) What were the mean litter sizes for the Balb and C57 mice? (2) How were the degrees of freedom (df) calculated? (3) What does P mean for your results? (4) Did you accept or reject your null hypothesis? (5) What can you conclude about the litter sizes for these two stains of mice? 10