Dr. O. Sophila, a close friend of Dr. Ara B. Dopsis, reviews the results Dr. Dopsis obtained in his experiment with iris plants described in Genetic Analysis 4.3. Dr. Sophila thinks the F₂ progeny demonstrate that a single gene with incomplete dominance has produced a 1:2:1 ratio. Dr. Dopsis insists his proposal of recessive epistasis producing a 9:4:3 ratio in the F₂ is correct. To test his proposal, Dr. Dopsis examines the F₂ data under the assumptions of the single-gene incomplete dominance model using chi-square analysis. Calculate and interpret this chi-square value. Can Dr. Dopsis reject the single-gene incomplete dominance model on the basis of this analysis? Explain why or why not.
Table of contents
- 1. Introduction to Genetics51m
- 2. Mendel's Laws of Inheritance3h 37m
- 3. Extensions to Mendelian Inheritance2h 41m
- 4. Genetic Mapping and Linkage2h 28m
- 5. Genetics of Bacteria and Viruses1h 21m
- 6. Chromosomal Variation1h 48m
- 7. DNA and Chromosome Structure56m
- 8. DNA Replication1h 10m
- 9. Mitosis and Meiosis1h 34m
- 10. Transcription1h 0m
- 11. Translation58m
- 12. Gene Regulation in Prokaryotes1h 19m
- 13. Gene Regulation in Eukaryotes44m
- 14. Genetic Control of Development44m
- 15. Genomes and Genomics1h 50m
- 16. Transposable Elements47m
- 17. Mutation, Repair, and Recombination1h 6m
- 18. Molecular Genetic Tools19m
- 19. Cancer Genetics29m
- 20. Quantitative Genetics1h 26m
- 21. Population Genetics50m
- 22. Evolutionary Genetics29m
3. Extensions to Mendelian Inheritance
Chi Square Analysis
Problem 7a
Textbook Question
If a chi-square test produces a chi-square value of 7.83 with 4 degrees of freedom,
In what interval range does the P value fall?

1
Step 1: Understand the problem. The chi-square test is used to determine whether there is a significant difference between the observed and expected data. Here, the chi-square value is 7.83, and the degrees of freedom (df) are 4. We need to determine the range of the P-value.
Step 2: Recall the relationship between the chi-square value, degrees of freedom, and the P-value. The P-value is determined by comparing the chi-square value to a chi-square distribution table for the given degrees of freedom.
Step 3: Locate the row in the chi-square distribution table corresponding to 4 degrees of freedom. Identify the chi-square values in this row that are closest to 7.83. These values will help determine the range of the P-value.
Step 4: Find the P-value intervals associated with the chi-square values identified in Step 3. The P-value decreases as the chi-square value increases, so the range will correspond to the interval between the two closest chi-square values.
Step 5: Conclude that the P-value falls within the interval determined in Step 4. This interval provides an estimate of the probability that the observed data could occur under the null hypothesis.

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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Chi-Square Test
The chi-square test is a statistical method used to determine if there is a significant association between categorical variables. It compares the observed frequencies in each category to the expected frequencies, which are calculated under the assumption of no association. A higher chi-square value indicates a greater discrepancy between observed and expected values.
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Degrees of Freedom
Degrees of freedom (df) in a chi-square test refer to the number of independent values that can vary in the analysis. For a chi-square test of independence, the degrees of freedom are calculated as (number of rows - 1) × (number of columns - 1). In this case, with 4 degrees of freedom, it indicates the complexity of the data being analyzed.
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Step 2
P-Value
The P-value is a measure that helps determine the significance of the results from a statistical test. It represents the probability of observing the test results, or something more extreme, under the null hypothesis. A lower P-value (typically less than 0.05) suggests that the observed data is unlikely under the null hypothesis, leading to its rejection.
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