Chi Squared 

Analysis Activity

Objective: To determine whether or not the difference between the expected allele frequencies and the observed allele frequencies is significant.

Directions: (Note: You must complete the Hardy-Weinberg Activity before doing this one)

1. Make sure you have:
   
 
a. A calculator
b. Hard copies of Tables 3 and 4
c. Hard copies of completed Table 2 from the  Hardy-Weinberg Activity
d. Hard copies of current project data
e.  Hard copies of the Chi Squared Table 
 
 
 
 
2. Based on the objective, your hypothesis is that there is no significant difference between the expected and observed allele frequencies.
   
3. Use the data from 1c-e  to complete Table 3.
 
4. Use the Chi Squared Table to find the probability associated with the Chi Squared value from the last row of Table 3.
   
5. Use Table 4 to summarize your findings.
   
6. For this project, assume that a probability greater than 10% (p > 0.1) means that the hypothesis is not accepted.

Questions:

1. Before you began this activity, did you think that  there would be significant differences between the expected and observed numbers of individuals for the six traits studied?
 
2. Restate your initial ideas in terms of accepting or rejecting the hypothesis.
 
3. For which of the six traits (or phenotypes) was the hypothesis rejected?
 
4. What reasons might account for any rejections?
 
5. Explain why you'd expect more discrepancies between your class (or school) data and the accepted data than between the data from all the schools and the accepted data.
 
6. Did your results match your expectations? Explain
 
7. Suppose you thought  that the alleles for each of the traits was distributed in the human population in accordance with the ratios predicted by Mendel's Law of Dominance. Write a hypothesis that you could use to test this idea.
 
8. Describe how you would carry out a procedure to test this hypothesis.
 
9. Based on the results of your calculations, would you expect that the allele frequencies from the next project run to be similar to the frequencies you found? Please explain.

References:

Chi Squared Table - Explanation of how the table works

The Chi-square goodness of fit test - Good  examples of how the Chi Squared analysis is used

The Chi Squared Test - The explanation includes reasoning for Yates correction for continuity

Expected Values and the c 2 Test - Lecture notes that clearly explain the Chi Squared analysis