Mendel's First Law
The Chi-Square Test
An important question to answer in any genetic experiment is how can we decide if our data fits any of the Mendelian ratios we have discussed. A statistical test that can test out ratios is the Chi-Square or Goodness of Fit test.
Degrees of freedom (df) = n-1 where n is the number of classes
Let's test the following data to determine if it fits a 9:3:3:1 ratio.
Number of classes (n) = 4
df = n-1 + 4-1 = 3
Chi-square value = 0.47
Enter the Chi-Square table at df = 3 and we see the probability of our chi-square value is greater than 0.90. By statistical convention, we use the 0.05 probability level as our critical value. If the calculated chi-square value is less than the 0 .05 value, we accept the hypothesis. If the value is greater than the value, we reject the hypothesis. Threrefore, because the calculated chi-square value is greater than the we accept the hypothesis that the data fits a 9:3:3:1 ratio.
A Chi-Square Table
Copyright © 2000. Phillip McClean