CHI-SQUARE (χ2) WORKSHEET



Name ________________________ Per. _____CHI-SQUARE (χ2) WORKSHEETGWHS AP BIOLOGYGenetics use a statistical test called a chi square test to see if the results of a cross match the expected results. The scientist states a null hypothesis is tested mathematically. The null hypothesis states that there is no difference between the observed ratio and the expected ratio.P generation: Round & Yellow x Wrinkled & Green F1: Round & Yellow x Wrinkled & Green (Testcross) (Genotypes) ____________ x ____________F2 Phenotypes: F2 Genotypes: Expected Ratio: = = = = = = = =Chi-Square Formula χ2 = Sum of -----------------------or χ2 = Σ --------(observed – expected)2expected(o – e)2eUse this table to calculate your chi-square.PhenotypeObserved (o)Expected (e)(o-e)(o-e)2(o-e)2---------eSum (Σ) = ______Degrees of Freedom (# of classes – 1) = _________P (from table) = ________Table of Chi-square values. To use this table find the location of your sum (Σ) on this table and read the corresponding P from the top row. *Biologists generally accept P=. 05 as the cutoff for accepting or rejecting a hypothesis.Degrees of FreedomP = .95P = .90P = .70P = .50P = .30P = .20P = .10P = .05P = .01P = .00110.0040.0160.150.461.071.642.713.846.6410.8320.100.210.711.392.413.224.615.999.2113.8230.350.581.422.373.674.646.257.8211.3516.2740.711.062.203.364.885.997.789.4913.2818.4751.151.613.004.356.067.299.2411.0715.0920.5261.642.203.835.357.238.5610.6512.5916.8122.4672.172.834.676.358.389.8012.014.0718.4824.3282.733.495.537.349.5211.0313.3615.5120.0926.13 Accept RejectCompare you calculated value to the value in the P=. 05 columns. If your calculated value is less then this value your results have a GREATER then a 95% chance of fitting the expected ratio. If your calculated value is greater than this value your results have LESS than a 95% chance of fitting the expected ratio.Question: Does your χ2 test result support the conclusion that the data fit the expected ratio? Explain. (Remember that biologists consider a P of .05 or less as statistically significant.)Name ________________________ Per. _____CHI-SQUARE (χ2) WORKSHEETGWHS AP BIOLOGYGenetics use a statistical test called a chi square test to see if the results of a cross match the expected results. The scientist states a null hypothesis is tested mathematically. The null hypothesis states that there is no difference between the observed ratio and the expected ratio.P generation: Brown Hair & No Freckles x Red Hair & Freckles F1: Brown & No Freckles x Red & Freckles (Testcross) (Genotypes) ____________ x ____________F2 Phenotypes: F2 Genotypes: Expected Ratio: = = = = = = = =Chi-Square Formula χ2 = Sum of -----------------------or χ2 = Σ --------(observed – expected)2expected(o – e)2eUse this table to calculate your chi-square.PhenotypeObserved (o)Expected (e)(o-e)(o-e)2(o-e)2---------eSum (Σ) = ______Degrees of Freedom (# of classes – 1) = _________P (from table) = ________Table of Chi-square values. To use this table find the location of your sum (Σ) on this table and read the corresponding P from the top row. *Biologists generally accept P=. 05 as the cutoff for accepting or rejecting a hypothesis.Degrees of FreedomP = .95P = .90P = .70P = .50P = .30P = .20P = .10P = .05P = .01P = .00110.0040.0160.150.461.071.642.713.846.6410.8320.100.210.711.392.413.224.615.999.2113.8230.350.581.422.373.674.646.257.8211.3516.2740.711.062.203.364.885.997.789.4913.2818.4751.151.613.004.356.067.299.2411.0715.0920.5261.642.203.835.357.238.5610.6512.5916.8122.4672.172.834.676.358.389.8012.014.0718.4824.3282.733.495.537.349.5211.0313.3615.5120.0926.13 Accept RejectCompare you calculated value to the value in the P=. 05 columns. If your calculated value is less then this value your results have a GREATER then a 95% chance of fitting the expected ratio. If your calculated value is greater than this value your results have LESS than a 95% chance of fitting the expected ratio.Question: Does your χ2 test result support the conclusion that the data fit the expected ratio? Explain. (Remember that biologists consider a P of .05 or less as statistically significant.) ................
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