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The Hypothesis The Hypothesis is a simple statement of the Genetic Inheritance of the trait(s) of interest. Example: Ÿ The trait is Simple Mendelian. Ÿ The traits have Duplicate Dominant Epistasis Ÿ The trait is Simple Mendelian with a Penetrance of 80% Ideally,The Hypothesis is created before the experiment. Often, you will conduct a preliminary experiment to determine The Hypothesis, then do a final experiment to test it. Hypothesis for the Experiment This is a statement of what we expect the results of experiment to be if The Hypothesis is correct. It will change, depending on the experiment used to test The Hypothesis. Examples: Ÿ The dihybrid cross gives a 3:1 ratio of Blue to Red Ÿ The monohybrid cross gives a 2:1 ratio of Agouti to Yellow Ÿ The trihybrid cross gives a 28:16:15:6:2 ratio. The Experiment The experiment is designed to be able to distinguish The Hypothesis from other possible alternatives. While the mono-, di-, tri-hybrid crosses are often used, many crosses are possible. Depending on the question, other experiments may be more powerful, e.g., the test cross is used when testing for linkage. The Data For Chi-Square Goodness of Fit Tests, the data consist of observed number of individuals with each of the traits. Which traits are expected and their frequencies depend on the Experimental Hypothesis. The data can be tabulated as: Phenotype Brown Albino Total Observed 80 20 100 Chi-Square Goodness of Fit Phenotype Brown Albino Total Expected Frequency 3/4 1/4 1 Chi-Square Goodness of Fit Phenotype Brown Albino Total Expected Frequency 3/4 1/4 1 Observed 80 20 100 Chi-Square Goodness of Fit Phenotype Brown Albino Total Expected Frequency 3/4 1/4 1 Observed Expected 80 75 20 25 100 100 Chi-Square Goodness of Fit Phenotype Brown Albino Total Expected Frequency 3/4 1/4 1 Observed Expected 80 75 20 25 100 100 O-E 5 -5 0 Chi-Square Goodness of Fit Phenotype Brown Albino Total Expected Frequency 3/4 1/4 1 Observed Expected 80 75 20 25 100 100 O-E 5 -5 0 (O−E ) 2 E 0.33 1 1.33 Chi Square Table Degrees of Freedom (df) Chi-Square (x 2 ) 1 3.84 2 5.99 3 7.82 4 5 6 7 9.49 11.07 12.59 14.07 Results of the Chi-Square Test Statistical Result: Ÿ If the calculated Chi-Square is greater than the tabled value, Reject the Hypothesis. Ÿ If the calculated Chi-Square is smaller than the tabled value, Fail to Reject the Hypothsis. Genetic Conclusion Relates back to The Hypothesis. If Reject the Hypothesis vThere is enough evidence from this experiment to conclude that Brown vs Albino is not Simple Mendelian. Genetic Conclusion Relates back to The Hypothesis. If Reject the Hypothesis vThere is enough evidence from this experiment to conclude that Brown vs Albino is not Simple Mendelian. If Fail to Reject the Hypothesis vSimple Mendelian Inheritance is consistent with this experiment. Example Genetic Situation Ÿ Flower Color in Snapdragons 3 colors: Purple Pink White Ÿ Hypothesis (Partial Dominance) Purple: WW Pink: Ww White: ww Example Genetic Situation Ÿ Flower Color in Snapdragons 3 colors: Purple Pink White Ÿ Hypothesis (Partial Dominance) Purple: WW Pink: Ww White: ww Experiment Ÿ Monohybrid Cross Expected Results: ¼ Purple ½ Pink ¼ White Results Phenotype Purple Pink White Total Observed Expected Chi-Square 345 329.25 705 658.5 267 329.25 1,317 1,317 7.32 Example Genetic Situation Ÿ Flower Color in Snapdragons 3 colors: Purple Pink White Ÿ Hypothesis (Partial Dominance) Purple: WW Pink: Ww White: ww Experiment Ÿ Monohybrid Cross Expected Results: ¼ Purple ½ Pink ¼ White Results Phenotype Purple Pink White Total Observed Expected Chi-Square 345 329.25 705 658.5 267 329.25 1,317 1,317 7.32 Conclusion Ÿ Statistical Conclusion 7.32 > 5.99 Reject the Hypothesis Ÿ Genetic Conclusion There is enough evidence from this experiment to conclude that purple flower color in snapdragons does not have Partial Dominance Inheritance