Chi-Square Analysis (11/1-11/4)

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Chi-Square Test (Hint: 2)

Used to determine if the results are due to chance

x² = the sum of ((observed – expected)²/expected)

Observed

The numbers of each phenotype resulting from an experimental cross

Expected

Predicted from the Mendelian ratios

Goodness-of-fit

How well does the data fit the expected hypothesis      

Null Hypothesis (Hint: 2)

There is NO significant difference between the observed and expected results

Random chance alone is responsible for the deviation between the observed and expected phenotypic ratios

Chi-Square Table: Across the Top (Hint: 2)

The probability (p) that the deviation from the expected is due to chance

Example: At the left: p = 0.995: 99.5% chance that the result is due to random chance

Chi-Square Table: In the Body (Hint: 3)

x² values that correspond with different probabilities

Small numbers correspond with high probability on the left

Large numbers correspond with low probability on the right

Degrees of Freedom (df) (Hint: 2)

x² tests have different numbers of components and will produce different numbers that correspond to the same probability

df = n-1 (n = number of categories (in this case the number of possible phenotypes))

What is the threshold for significance?

p < 0.05