In this lesson you have learned how to calculate a statistical analysis known as chi-square to determine if the differences seen between expected and observed numbers of resistant and susceptible tomato plants was significant. We have talked about how to accurately interpret results and the impact it has on our experimental hypothesis. We looked at both a phenotyping and genotyping example, as well as some computer-aided tools. Finally, the strengths and weaknesses of using the chi-square test in plant breeding applications were discussed briefly.