Chi Square and Linkage Video Lessons

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Problem: Dr. Ara B. Dopsis and Dr. C. Ellie Gans are performing genetic crosses on daisy plants. They self-fertilize a blue-flowered daisy and grow 100 progeny plants that consist of 55 blue-flowered plants, 22 purple-flowered plants, and 23 white-flowered plants.Dr. Dopsis believes this is the result of segregation of two alleles at one locus and that the progeny ratio is 1:2:1. Dr. Gans thinks the progeny phenotypes are the result of two epistatic genes and that the ratio is 9:3:4.The two scientists ask you to resolve their conflict by performing chi-square analysis on the data for both proposed genetic mechanisms: 1) Calculate the chi-square value for hypothesis of segregation of two alleles at one locus. 2) Calculate the chi-square value for hypothesis of interaction of two epistatic genes. 3) Based on chi-square analysis, what is your conclusion regarding these two genetic hypotheses?

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Part 1: Null hypothesis: Segregation of two alleles in one locus is observed.

Expected Phenotypic Ratio: 1:2:1

Total number of offsprings = 100 flowers


Expected blue-flowered plants = 100×21+2+1 = 50 flowers


Expected purple-flowered plants = 100×11+2+1 = 25 flowers


Expected white-flowered plants = 100×11+2+1 = 30 flowers


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Problem Details

Dr. Ara B. Dopsis and Dr. C. Ellie Gans are performing genetic crosses on daisy plants. They self-fertilize a blue-flowered daisy and grow 100 progeny plants that consist of 55 blue-flowered plants, 22 purple-flowered plants, and 23 white-flowered plants.

Dr. Dopsis believes this is the result of segregation of two alleles at one locus and that the progeny ratio is 1:2:1. Dr. Gans thinks the progeny phenotypes are the result of two epistatic genes and that the ratio is 9:3:4.

The two scientists ask you to resolve their conflict by performing chi-square analysis on the data for both proposed genetic mechanisms: 

1) Calculate the chi-square value for hypothesis of segregation of two alleles at one locus. 

2) Calculate the chi-square value for hypothesis of interaction of two epistatic genes. 

3) Based on chi-square analysis, what is your conclusion regarding these two genetic hypotheses?

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What scientific concept do you need to know in order to solve this problem?

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Based on our data, we think this problem is relevant for Professor Bardwell's class at UCI.