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## Chi-Square Test

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**We have discussed predicting allele, genotype, and phenotype**frequency using the Hardy-Weinberg equation • But how much of a “deviation” is actually significant? • One way is to use a chi-square (χ2) test • Essentially, if data deviates from predicted values too much, the χ2 statistic will exceed a certain value**χ2 =**• When this is computed, it is compared to established χ2 which have been calculated based solely on chance • The values are based on the degrees of freedom • If it is exceeded, we reject the hypothesis**Example**The number of expected flowers of red, pink, and white phenotypes is listed below, along with the observed values. We hypothesize that the observed values are within statistical norms. Do a chi-square test to confirm or deny the hypothesis**Answer**• Use the equation: χ2 = = = 0.875 The critical value is 5.991, so the hypothesis is not rejected.