Pollen from a pure-bred tomato plant with white flowers and yellow fruit was transferred to the stigmas of a pure-bred plant with yellow flowers and red fruit. All the F1Â generation had yellow flowers and red fruit.Â
Pollen from the F1Â generation was transferred to pure-bred plants with white flowers and yellow fruit. The ratio of phenotypes expected among the offspring of a dihybrid test cross such as this is 1:1:1:1.
Seeds from the plants were collected and grown, giving plants with the following phenotypes:
- Yellow flowers and red fruit: 59
- Yellow flowers and yellow fruit: 56
- White flowers and red fruit: 40
- White flowers and yellow fruit: 45
- Total number of plants in the four categories: 200
A chi-squared (χ2) test can be carried out to check whether the numbers of each phenotype of offspring resulting from the test cross are in agreement with a 1:1:1:1 ratio.Â
The chi-squared (χ2) equation and distribution is as follows:
Degrees of freedom |
Probability (p) |
0.10 |
0.05 |
0.02 |
0.01 |
0.001 |
1 |
2.71 |
3.84 |
5.41 |
6.64 |
10.83 |
2 |
4.61 |
5.99 |
7.82 |
9.21 |
13.82 |
3 |
6.25 |
7.82 |
9.84 |
11.35 |
16.27 |
4 |
7.78 |
9.49 |
11.67 |
13.28 |
18.47 |
Use this information to produce a statistical conclusion about the difference between the expected and actual results in the tomato breeding experiment.
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