AP Biology: Chi-Square Practice
Offspring of certain fruit flies may have yellow or ebony bodies and normal wings or short wings.
Genetic theory predicts that these traits will appear in the ratio 9:3:3:1 (yellow and normal, yellow and
short, ebony and normal, ebony and short). A researcher checks 100 such flies and finds the distribution
of traits to be 59, 20, 11, and 10 respectively. Are the results consistent with the theoretical distribution
predicted by the genetic model?
1. State your null hypothesis
2. What are the expected counts? (Hint: We expect 9/16 of the 100 flies to have yellow and normal
wings.
3. What is your Chi Square value?
Observed
Expected
(o-e)2
e
Yellow & Normal Yellow & Short
Ebony & Normal Ebony & Short
Total
59
11
100
20
10
4. How many degrees of freedom do you have?
5. Refer to the Chi-Square table to figure out your critical value.
6. Do you reject your null hypothesis?
7. Are the results consistent with the theoretical distribution predicted by the genetic model?