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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 15b
Chapter 4, Problem 15b

A plant line with reduced fertility comes to the attention of a plant breeder who observes that seed pods often contain a mixture of viable seeds that can be planted to produce new plants and withered seeds that cannot be sprouted. The breeder examines numerous seed pods in the reduced fertility line and counts 622 viable seeds and 204 nonviable seeds.
Propose an additional experiment to test the genetic mechanism you propose. If your hypothesis is correct, what experimental outcome do you predict?

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Propose a hypothesis: Based on the observation of viable and nonviable seeds, hypothesize that the reduced fertility may be due to a genetic mechanism such as a recessive lethal allele. This allele could cause nonviable seeds when present in a homozygous state.
Design an experiment: Cross plants from the reduced fertility line with plants from a wild-type line that does not exhibit reduced fertility. This will allow you to observe the inheritance pattern of the viable and nonviable seeds in the offspring.
Predict the outcome: If the hypothesis of a recessive lethal allele is correct, the offspring from the cross should show a Mendelian ratio of 2:1 for viable to nonviable seeds. This is because the homozygous recessive genotype would result in nonviable seeds, while the heterozygous and homozygous dominant genotypes would produce viable seeds.
Perform the cross and collect data: Allow the plants to self-pollinate or cross-pollinate as per the experimental design. Count the number of viable and nonviable seeds in the offspring to determine if the observed ratio matches the predicted 2:1 ratio.
Analyze the results: Use a chi-square test to compare the observed ratio of viable to nonviable seeds with the expected 2:1 ratio. If the chi-square test supports the hypothesis, it provides evidence for the proposed genetic mechanism. If not, consider alternative hypotheses and repeat the experiment with modifications.

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Key Concepts

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

Genetic Inheritance

Genetic inheritance refers to the process by which traits and characteristics are passed from parents to offspring through genes. Understanding inheritance patterns, such as Mendelian ratios, is crucial for predicting the outcomes of breeding experiments. In this case, the ratio of viable to nonviable seeds may suggest a genetic basis for fertility issues, potentially indicating dominant or recessive traits affecting seed viability.
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Phenotypic Variation

Phenotypic variation is the observable differences in traits among individuals in a population, which can arise from genetic differences, environmental factors, or a combination of both. In the context of the plant line, the presence of both viable and nonviable seeds indicates phenotypic variation that may be linked to underlying genetic mechanisms. Analyzing this variation can help identify specific traits associated with fertility.
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Experimental Design

Experimental design is the process of planning an experiment to ensure that it effectively tests a hypothesis. In this scenario, the breeder could conduct a controlled cross between the reduced fertility line and a known fertile line to observe the inheritance of seed viability. The predicted outcome, if the hypothesis is correct, would be a specific ratio of viable to nonviable seeds in the offspring, supporting the proposed genetic mechanism.
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Related Practice
Textbook Question

Total cholesterol in blood is reported as the number of milligrams (mg) of cholesterol per 100 milliliters (mL) of blood. The normal range is 180–220 mg/100 mL. A gene mutation altering the function of cell-surface cholesterol receptors restricts the ability of cells to collect cholesterol from blood and draw it into cells. This defect results in elevated blood cholesterol levels. Individuals who are heterozygous for a mutant allele and a wild-type allele have levels of 300–600 mg/100 mL, and those who are homozygous for the mutation have levels of 800–1000 mg/100 mL. Identify the genetic term that best describes the inheritance of this form of elevated cholesterol level, and justify your choice.

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Textbook Question

Flower color in snapdragons results from the amount of the pigment anthocyanin in the petals. Red flowers are produced by plants that have full anthocyanin production, and ivory-colored flowers are produced by plants that lack the ability to produce anthocyanin. The allele An1 has full activity in anthocyanin production, and the allele An2 is a null allele. Dr. Ara B. Dopsis, a famous genetic researcher, crosses pure-breeding red snapdragons to pure-breeding ivory snapdragons and produces F₁ progeny plants that have pink flowers. He proposes that this outcome is the result of incomplete dominance, and he crosses the F₁ to test his hypothesis. What phenotypes does Dr. Dopsis predict will be found in the F₂, and in what proportions?

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Textbook Question

A plant line with reduced fertility comes to the attention of a plant breeder who observes that seed pods often contain a mixture of viable seeds that can be planted to produce new plants and withered seeds that cannot be sprouted. The breeder examines numerous seed pods in the reduced fertility line and counts 622 viable seeds and 204 nonviable seeds.

What single-gene mechanism best explains the breeder's observation?

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Textbook Question

In cattle, an autosomal mutation called Dexter produces calves with short stature and short limbs. Embryos that are homozygous for the Dexter mutation have severely stunted development and either spontaneously abort or are stillborn. What progeny phenotypes do you expect from the cross of two Dexter cows? What are the expected proportions of the expected phenotypes?

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Textbook Question

The coat color in mink is controlled by two codominant alleles at a single locus. Red coat color is produced by the genotype R₁R₁, silver coat by the genotype R₁R₂, and platinum color by R₂R₂. White spotting of the coat is a recessive trait found with the genotype ss. Solid coat color is found with the S– genotype.


What are the expected progeny phenotypes and proportions for the cross SsR₁R₂ x ssR₂R₂?

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Textbook Question

The coat color in mink is controlled by two codominant alleles at a single locus. Red coat color is produced by the genotype R₁R₁, silver coat by the genotype R₁R₂, and platinum color by R₂R₂. White spotting of the coat is a recessive trait found with the genotype ss. Solid coat color is found with the S– genotype.


If the cross SsR₁R₂ x SsR₁R₁ is made, what are the progeny phenotypes, and in what proportions are they expected to occur?

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