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Ch. 4 - Gene Interaction
Sanders - Genetic Analysis: An Integrated Approach 3rd Edition
Sanders3rd EditionGenetic Analysis: An Integrated ApproachISBN: 9780135564172Not the one you use?Change textbook
All textbooksSanders 3rd EditionCh. 4 - Gene InteractionProblem 30a
Chapter 4, Problem 30a

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. For each proposed mechanism, fill in the values requested on the form the researchers have provided for your analysis.
Use the form below to calculate chi-square for the 1:2:1 hypothesis of Dr. Sophila.
Table displaying observed and expected phenotypes for a chi-square analysis of daisy plant genetics.

Verified step by step guidance
1
Step 1: Understand the problem. The goal is to determine which hypothesis (1:2:1 or 9:3:4) better explains the observed data using chi-square analysis. The observed data consists of 55 blue-flowered plants, 22 purple-flowered plants, and 23 white-flowered plants. For the 1:2:1 hypothesis, the expected ratio is 1:2:1, and for the 9:3:4 hypothesis, the expected ratio is 9:3:4.
Step 2: Calculate the total number of progeny. Add the observed counts: 55 (blue) + 22 (purple) + 23 (white) = 100. This total will be used to calculate the expected numbers for each phenotype based on the proposed ratios.
Step 3: Calculate the expected numbers for the 1:2:1 hypothesis. Divide the total number of progeny (100) according to the 1:2:1 ratio. For blue-flowered plants, the expected number is (1/4) * 100. For purple-flowered plants, the expected number is (2/4) * 100. For white-flowered plants, the expected number is (1/4) * 100.
Step 4: Use the chi-square formula to calculate the chi-square value for the 1:2:1 hypothesis. The formula is: χ² = Σ((Oᵢ - Eᵢ)² / Eᵢ), where Oᵢ is the observed number for each phenotype, and Eᵢ is the expected number for each phenotype. Perform this calculation for each phenotype (blue, purple, white) and sum the results.
Step 5: Compare the calculated chi-square value to the critical value from a chi-square distribution table. Use the appropriate degrees of freedom (df = number of categories - 1) and a significance level (commonly 0.05). If the chi-square value is less than the critical value, the 1:2:1 hypothesis is supported. Otherwise, it is rejected in favor of the alternative hypothesis.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Mendelian Genetics

Mendelian genetics is the study of how traits are inherited through the segregation and independent assortment of alleles. It is based on Gregor Mendel's principles, which describe how dominant and recessive alleles interact to produce observable traits in offspring. Understanding these principles is crucial for analyzing genetic crosses and predicting progeny ratios.
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Descriptive Genetics

Chi-Square Analysis

Chi-square analysis is a statistical method used to determine if there is a significant difference between observed and expected frequencies in categorical data. In genetics, it helps assess whether the observed ratios of phenotypes in progeny fit the expected ratios based on a specific genetic hypothesis. This analysis is essential for validating or refuting the proposed genetic mechanisms.
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Chi Square Analysis

Epistasis

Epistasis refers to the interaction between genes, where the expression of one gene is affected by one or more other genes. This can lead to modified phenotypic ratios that differ from those predicted by Mendelian inheritance alone. Understanding epistasis is important for interpreting complex inheritance patterns, such as the 9:3:4 ratio proposed by Dr. Gans.
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Related Practice
Textbook Question

Marfan syndrome is an autosomal dominant disorder in humans. It results from mutation of a gene on chromosome 15 that produces the connective tissue protein fibrillin. In its wild-type form, fibrillin gives connective tissues, such as cartilage, elasticity. When mutated, however, fibrillin is rigid and produces a range of phenotypic complications, including excessive growth of the long bones of the leg and arm, sunken chest, dislocation of the lens of the eye, and susceptibility to aortic aneurysm, which can lead to sudden death in some cases. Different sets of symptoms are seen among various family members, as shown in the pedigree below. Each quadrant of the circles and squares represents a different symptom, as the key indicates.

All cases of Marfan syndrome are caused by mutation of the fibrillin gene, and all family members with Marfan syndrome carry the same mutant allele. What do the differences shown in the phenotypes of family members say about the expression of the mutant allele?

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Textbook Question

Yeast are single-celled eukaryotic organisms that grow in culture as either haploids or diploids. Diploid yeast are generated when two haploid strains fuse together. Seven haploid mutant strains of yeast exhibit similar normal growth habit at 25°C, but at 37°C, they show different growth capabilities. The table below displays the growth pattern.

Hypothesize about the nature of the mutation affecting each of these mutant yeast strains, including why strains B and G display different growth habit at 37°C than the other strains.

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Textbook Question

Yeast are single-celled eukaryotic organisms that grow in culture as either haploids or diploids. Diploid yeast are generated when two haploid strains fuse together. Seven haploid mutant strains of yeast exhibit similar normal growth habit at 25°C, but at 37°C, they show different growth capabilities. The table below displays the growth pattern.

Researchers induce fusion in pairs of haploid yeast strains (all possible combinations), and the resulting diploids are tested for their ability to grow at 37°C. The results of the growth experiment are shown below. How many different genes are mutated among these seven yeast strains? Identify the strains that represent each gene mutation.

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Textbook Question

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. For each proposed mechanism, fill in the values requested on the form the researchers have provided for your analysis.

Use the form below to calculate chi-square for the 9:3:4 hypothesis of Dr. Gans.

437
views
Textbook Question

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. For each proposed mechanism, fill in the values requested on the form the researchers have provided for your analysis.


What is your conclusion regarding these two genetic hypotheses: the 1:2:1 hypothesis and the 9:3:4 hypothesis?

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Textbook Question

Human ABO blood type is determined by three alleles, two of which (I^A and I^B) produce gene products that modify the H antigen produced by protein activity of an independently assorting H gene. A rare abnormality known as the 'Bombay phenotype' is the result of epistatic interaction between the gene for the ABO blood group and the H gene. Individuals with the Bombay phenotype appear to have blood type O based on the inability of both anti-A antibody and anti-B antibody to detect an antigen. The apparent blood type O in Bombay phenotype is due to the absence of H antigen as a result of homozygous recessive mutations of the H gene. Individuals with the Bombay phenotype have the hh genotype. Use the information above to make predictions about the outcome of the cross shown below.

IᴬIᴮHh×IᴬIᴮHh

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