Ch. 4 - Modification of Mendelian Ratios

Klug - Essentials of Genetics 10th Edition

Klug10th EditionEssentials of GeneticsISBN: 9780135588789Not the one you use?Change textbook

Klug 10th Edition

Ch. 4 - Modification of Mendelian Ratios

Problem 19

Chapter 4, Problem 19

In another cross, the frog geneticist from Problem 18 mated two purple, utterers with the results shown here. What were the genotypes of the parents? <IMAGE>

Verified step by step guidance

Identify the phenotype and genotype relationship for the trait in question. Since the parents are described as 'purple, utterers,' determine whether purple is dominant or recessive and what genotypes correspond to the purple phenotype.

Analyze the offspring phenotypes and their ratios from the cross. Use the phenotypic ratios to infer the possible genotypes of the parents by comparing expected Mendelian ratios for different genotype combinations.

Set up a Punnett square for the possible parental genotype combinations that could produce the observed offspring phenotypes and ratios. This will help visualize the expected genotypic and phenotypic outcomes.

Compare the predicted offspring genotypes and phenotypes from the Punnett square with the actual offspring data given in the problem. Narrow down the parental genotypes to those that best fit the observed results.

Conclude the most likely genotypes of the parents based on the analysis, ensuring that the predicted offspring ratios match the observed data.

Key Concepts

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

Mendelian Inheritance and Genotype Determination

Mendelian inheritance explains how traits are passed from parents to offspring through dominant and recessive alleles. Understanding genotype combinations helps predict offspring phenotypes and genotypes based on parental alleles, using principles like segregation and independent assortment.

Phenotype vs. Genotype

Phenotype refers to the observable traits of an organism, while genotype is the genetic makeup underlying those traits. Distinguishing between the two is essential for interpreting crosses, as different genotypes can produce the same phenotype, especially when dominant alleles are involved.

Punnett Squares and Genetic Cross Analysis

Punnett squares are tools used to visualize and predict the outcome of genetic crosses by mapping possible allele combinations. They help determine the probability of offspring genotypes and phenotypes, which is crucial for deducing parental genotypes from observed progeny ratios.

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Related Practice

Textbook Question

A geneticist from an alien planet that prohibits genetic research brought with him to Earth two pure-breeding lines of frogs. One line croaks by uttering 'rib-it rib-it' and has purple eyes. The other line croaks more softly by muttering 'knee-deep knee-deep' and has green eyes. With a newfound freedom of inquiry, the geneticist mated the two types of frogs, producing F₁ frogs that were all utterers and had blue eyes. A large F₂ generation then yielded the following ratios:

27/64 blue-eyed, 'rib-it' utterer

12/64 green-eyed, 'rib-it' utterer

9/64 blue-eyed, 'knee-deep' mutterer

9/64 purple-eyed, 'rib-it' utterer

4/64 green-eyed, 'knee-deep' mutterer

3/64 purple-eyed, 'knee-deep' mutterer

Of these, how many are controlling eye color? How can you tell? How many are controlling croaking?

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Textbook Question

27/64 blue-eyed, 'rib-it' utterer

12/64 green-eyed, 'rib-it' utterer

9/64 blue-eyed, 'knee-deep' mutterer

9/64 purple-eyed, 'rib-it' utterer

4/64 green-eyed, 'knee-deep' mutterer

3/64 purple-eyed, 'knee-deep' mutterer

Assign gene symbols for all phenotypes and indicate the genotypes of the P₁ and F₁ frogs.

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Textbook Question

27/64 blue-eyed, 'rib-it' utterer

12/64 green-eyed, 'rib-it' utterer

9/64 blue-eyed, 'knee-deep' mutterer

9/64 purple-eyed, 'rib-it' utterer

4/64 green-eyed, 'knee-deep' mutterer

3/64 purple-eyed, 'knee-deep' mutterer

Indicate the genotypes of the six F₂ phenotypes.

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Textbook Question

Consider the three pedigrees below, all involving a single human trait.

Which combination of conditions, if any, can be excluded? dominant and X-linked dominant and autosomal recessive and X-linked recessive and autosomal

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Textbook Question

Consider the three pedigrees below, all involving a single human trait.

For each combination that you excluded, indicate the single individual in generation II (e.g., II-1, II-2) that was most instrumental in your decision to exclude it. If none were excluded, answer 'none apply.'

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