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Ch. 4 - Extensions of Mendelian Genetics
Klug - Concepts of Genetics  12th Edition
Klug12th EditionConcepts of Genetics ISBN: 9780135564776Not the one you use?Change textbook
Chapter 4, Problem 11

In rabbits, a series of multiple alleles controls coat color in the following way: C is dominant to all other alleles and causes full color. The chinchilla phenotype is due to the cch allele, which is dominant to all alleles other than C. The ch allele, dominant only to (albino), results in the Himalayan coat color. Thus, the order of dominance is C > cch > ch > ca. For each of the following three cases, the phenotypes of the P1 generations of two crosses are shown, as well as the phenotype of one member of the F1 generation.
Table showing rabbit coat color crosses with P₁ phenotypes, resulting F₁ phenotypes, and unknown F₁ cross outcomes.
For each case, determine the genotypes of the P1 generation and the F1 offspring, and predict the results of making each indicated cross between F1 individuals.

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Step 1: Understand the hierarchy of dominance for the alleles controlling coat color in rabbits. The dominance order is C > c^ch > c^h > c^a. This means that the C allele is dominant to all others, c^ch is dominant to c^h and c^a, c^h is dominant to c^a, and c^a is recessive to all other alleles.
Step 2: Analyze the phenotypes of the P₁ generation in each case. Use the dominance hierarchy to deduce the possible genotypes of the P₁ individuals. For example, if a rabbit has a full-color phenotype, it must have at least one C allele. If a rabbit has a chinchilla phenotype, it must have at least one c^ch allele but no C allele, and so on.
Step 3: Examine the phenotype of the F₁ offspring provided for each case. Use this information to confirm or refine the genotypes deduced for the P₁ generation. For example, if the F₁ offspring has a phenotype that could only result from a specific combination of alleles, this helps narrow down the possible genotypes of the P₁ parents.
Step 4: Predict the genotypes of the F₁ individuals resulting from the P₁ cross. Use a Punnett square to determine the possible combinations of alleles in the F₁ generation. For each combination, determine the phenotype based on the dominance hierarchy.
Step 5: Predict the results of the indicated cross between F₁ individuals. Construct a Punnett square using the genotypes of the F₁ individuals to determine the possible genotypes and phenotypes of the F₂ generation. For each genotype, assign the corresponding phenotype based on the dominance hierarchy.

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Key Concepts

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

Multiple Alleles

Multiple alleles refer to the presence of more than two alleles for a particular gene within a population. In the case of rabbit coat color, there are four alleles (C, c^ch, c^h, c^a) that determine the phenotype. Understanding how these alleles interact and their dominance hierarchy is crucial for predicting the phenotypes of offspring in genetic crosses.
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Dominance Hierarchy

Dominance hierarchy describes the relationship between alleles in terms of their expression in the phenotype. In this scenario, the order of dominance is C > c^ch > c^h > c^a, meaning that the C allele will mask the effects of all other alleles, while c^ch can mask c^h and c^a, and so forth. This hierarchy is essential for determining the expected phenotypes of the offspring based on the genotypes of the parents.
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Punnett Square

A Punnett square is a diagram used to predict the genotypes and phenotypes of offspring from genetic crosses. By organizing the possible gametes from each parent, it allows for a visual representation of how alleles combine. In this question, constructing Punnett squares for the F₁ generation will help in predicting the outcomes of the indicated crosses based on the established dominance relationships.
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Related Practice
Textbook Question

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Textbook Question

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Textbook Question

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Textbook Question

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From the results given above, determine the mode of inheritance by assigning gene symbols and indicating which genotypes yield which phenotypes.

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