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Ch. 3 - Mendelian Genetics
Klug - Concepts of Genetics 12th Edition
Klug12th EditionConcepts of Genetics ISBN: 9780135564776Not the one you use?Change textbook
All textbooksKlug 12th EditionCh. 3 - Mendelian GeneticsProblem 26a
Chapter 3, Problem 26a

Datura stramonium (the Jimsonweed) expresses flower colors of purple and white and pod textures of smooth and spiny. The results of two crosses in which the parents were not necessarily true breeding are shown below. Based on these results, put forward a hypothesis for the inheritance of the purple/white and smooth/spiny traits.

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1
Examine the phenotypic ratios in the offspring for each cross. Determine if the ratios suggest Mendelian inheritance patterns, such as a 3:1 ratio for a single gene with two alleles or a 9:3:3:1 ratio for two independently assorting genes.
Hypothesize whether each trait (flower color and pod texture) is controlled by a single gene with two alleles or multiple genes. For example, purple vs. white flowers might be controlled by a dominant and recessive allele of one gene.
Analyze whether the traits are inherited independently or if they are linked. If the phenotypic ratios deviate from expected Mendelian ratios, consider the possibility of genetic linkage or epistasis.
Propose a genetic model for each trait. For example, suggest that flower color is determined by a gene where the purple allele (P) is dominant to the white allele (p), and pod texture is determined by a gene where the spiny allele (S) is dominant to the smooth allele (s).
Test the hypothesis by predicting the expected phenotypic ratios for each cross based on the proposed genetic model. Compare these predictions to the observed results to evaluate the validity of the hypothesis.

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Key Concepts

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

Mendelian Inheritance

Mendelian inheritance refers to the principles of heredity established by Gregor Mendel, which include the concepts of dominant and recessive traits. In this context, traits such as flower color and pod texture can be analyzed to determine which traits are dominant and how they segregate during gamete formation. Understanding these principles is essential for hypothesizing the inheritance patterns observed in Datura stramonium.
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Phenotype and Genotype

The phenotype is the observable physical or biochemical characteristics of an organism, while the genotype is the genetic constitution that determines these traits. In the case of Datura stramonium, the purple and white flower colors, as well as smooth and spiny pod textures, represent different phenotypes that arise from specific genotypes. Analyzing the relationship between these two concepts is crucial for formulating a hypothesis about trait inheritance.
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Punnett Square

A Punnett square is a diagram used to predict the genetic outcomes of a cross between two organisms. It helps visualize the possible combinations of alleles from the parents and can indicate the expected ratios of phenotypes in the offspring. Utilizing a Punnett square can aid in hypothesizing the inheritance patterns of the purple/white flower colors and smooth/spiny pod textures in Datura stramonium based on the provided cross results.
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Related Practice
Textbook Question

A 'wrongful birth' case was recently brought before a court in which a child with Smith–Lemli–Opitz syndrome was born to apparently healthy parents. This syndrome is characterized by a cluster of birth defects including cleft palate, and an array of problems with the reproductive and urinary organs. Originally considered by their physician as having a nongenetic basis, the parents decided to have another child, who was also born with Smith–Lemli–Opitz syndrome. In the role of a genetic counselor, instruct the court about what occurred, including the probability of the parents having two affected offspring, knowing that the disorder is inherited as a recessive trait. Calculate the probability that both the male and female are carriers for TSD.

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Textbook Question

A 'wrongful birth' case was recently brought before a court in which a child with Smith–Lemli–Opitz syndrome was born to apparently healthy parents. This syndrome is characterized by a cluster of birth defects, including cleft palate, and an array of problems with the reproductive and urinary organs. Originally considered by their physician as having a nongenetic basis, the parents decided to have another child, who was also born with Smith–Lemli–Opitz syndrome. In the role of a genetic counselor, instruct the court about what occurred, including the probability of the parents having two affected offspring, knowing that the disorder is inherited as a recessive trait. What is the probability that neither of them is a carrier?

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Textbook Question

A 'wrongful birth' case was recently brought before a court in which a child with Smith–Lemli–Opitz syndrome was born to apparently healthy parents. This syndrome is characterized by a cluster of birth defects including cleft palate, and an array of problems with the reproductive and urinary organs. Originally considered by their physician as having a nongenetic basis, the parents decided to have another child, who was also born with Smith–Lemli–Opitz syndrome. In the role of a genetic counselor, instruct the court about what occurred, including the probability of the parents having two affected offspring, knowing that the disorder is inherited as a recessive trait. What is the probability that one of them is a carrier and the other is not? [Hint: The p values in (b), (c), and (d) should equal 1.]

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Textbook Question

Datura stramonium (the Jimsonweed) expresses flower colors of purple and white and pod textures of smooth and spiny. The results of two crosses in which the parents were not necessarily true breeding are shown below. Assuming that true-breeding strains of all combinations of traits are available, what single cross could you execute and carry to an F₂ generation that will prove or disprove your hypothesis? Assuming your hypothesis is correct, what results of this cross will support it?

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Textbook Question

The wild-type (normal) fruit fly, Drosophila melanogaster, has straight wings and long bristles. Mutant strains have been isolated that have either curled wings or short bristles. The genes representing these two mutant traits are located on separate chromosomes. Carefully examine the data from the following five crosses.

Identify each mutation as either dominant or recessive. In each case, indicate which crosses support your answer.

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Textbook Question

The wild-type (normal) fruit fly, Drosophila melanogaster, has straight wings and long bristles. Mutant strains have been isolated that have either curled wings or short bristles. The genes representing these two mutant traits are located on separate chromosomes. Carefully examine the data from the following five crosses.

Assign gene symbols and, for each cross, determine the genotypes of the parents.

871
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