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A-Level Biology OCR A

Chi Squared Significant Chi Squared Critical Hypothesis Expect Find

A chi-squared test determines if genetic cross data supports a hypothesis. It involves stating the null hypothesis, finding expected ratios, calculating chi-squared, finding the critical value, and comparing. If chi-squared is less than the critical value, there is no significant difference.

Un test du chi carré permet de déterminer si les données d'un croisement génétique soutiennent une hypothèse. Il faut énoncer l'hypothèse nulle, trouver les ratios attendus, calculer le chi carré, trouver la valeur critique et comparer. Si le chi carré est inférieur à la valeur critique, il n'y a pas de différence significative.

Front Describe how to conduct a chi-squared test to determine whether data from a genetic cross supports the hypothesis about how the characteristic is inherited.
Back Chi-squared test:
  • State null hypothesis - no significant dfference between what we expect and what we observe
  • Find expected ratios of each gamete combination using a Punnett square
  • Work out how many individuals of each phenotype you would expect acording to those ratios
  • Use the formula for chi-squared (degrees of freedom is n-1 where n is the number of categories/phenotypes)
  • Find the minimum chi squared value that gives a 5% probability in the table of values - critical value
  • If chi squared is less than critical value - no significant difference
  • If chi squared is greater than or equal to the critical value - significant difference

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