1. Chi-Squared
AP Biology

2. 1. Determine number of each phenotype observed and how many would be expected given basic genetic theory
2. Calculate chi-square statistic using this formula. You need to memorize the formula!
- “Χ” is Greek letter chi
- “∑” is a sigma; it means to sum the following terms for all phenotypes “obs” is the number of individuals of the given phenotype observed “exp” is the number of that phenotype expected from the null hypothesis.
Note that you must use the number of individuals, the counts, and NOT proportions, ratios, or frequencies.
3. State conclusion
If p value for calculate x2 is p > 0.05, ACCEPT your hypothesis
Ex: If p=.0.6, then there is a 60% chance your results are due to chance, NOT something else
If p value for calculate x2 is p < 0.05, REJECT your hypothesis
Ex: If p=0.01 then there is a 1% chance your results are due to chance, so there’s probably something else going on
Formula

3. Chi-Square Table