In the fruit fly Drosophila melanogaster, two genes control eye color and wing shape:
A geneticist crossed two Drosophila flies that were heterozygous for both genes (EeVvEeVvEeVv). The expected phenotypic ratio of their offspring under the hypothesis of independent assortment is 9:3:3:19:3:3:19:3:3:1.
The geneticist obtained a total of 320320320 offspring from this cross. The observed numbers for each phenotype were:
Use the chi-squared formula
χ2=∑(O−E)2E \chi^2 = \sum \frac{(O - E)^2}{E} χ2=∑E(O−E)2to calculate the χ2\chi^2χ2 value for these data.
State the number of degrees of freedom for this test.
Using the critical values table below (for p=0.05p = 0.05p=0.05), determine whether the null hypothesis (that there is no significant difference between the observed and expected results) should be accepted or rejected, and explain your answer.
| Degrees of freedom | Critical value (p=0.05p = 0.05p=0.05) |
|---|---|
| 1 | 3.84 |
| 2 | 5.99 |
| 3 | 7.82 |
| 4 | 9.49 |
