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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 \(c^{\mathrm{ch}}\) allele, which is dominant to all alleles other than \(C\). The \(c^{h}\) allele, dominant only to \(c^{a}\) (albino), results in the Himalayan coat color. Thus, the order of dominance is \(C>c^{\mathrm{dh}}>c^{h}>c^{a} .\) For each of the fol- lowing three cases, the phenotypes of the \(\mathrm{P}_{1}\) generations of two crosses are shown, as well as the phenotype of one member of the \(\mathrm{F}_{1}\) generation. For each case, determine the genotypes of the \(P_{1}\) generation and the \(\mathrm{F}_{1}\) offspring, and predict the results of making each indicated cross between \(F_{1}\) individuals.

Short Answer

Expert verified
Answer: Case 1 (Chinchilla x Chinchilla): P1 Generation: Genotypes - \(c^{\mathrm{ch}}c^{\mathrm{ch}}\) for both rabbits, Phenotypes - Chinchilla for both rabbits. F1 Generation: Genotypes - \(c^{\mathrm{ch}}c^{\mathrm{ch}}\) for all offspring, Phenotypes - Chinchilla for all offspring. Case 2 (Full color x Himalayan): P1 Generation: Genotypes - \(Cc^{\mathrm{h}}\) for the full-color rabbit and \(c^{\mathrm{h}}c^{\mathrm{h}}\) for the Himalayan rabbit, Phenotypes - Full color for one rabbit, Himalayan for the other rabbit. F1 Generation: Genotypes - \(Cc^{\mathrm{h}}\) for all offspring, Phenotypes - Full color for all offspring. Case 3 (Himalayan x Himalayan): P1 Generation: Genotypes - \(c^{\mathrm{h}}c^{\mathrm{h}}\) for both rabbits, Phenotypes - Himalayan for both rabbits. F1 Generation: Genotypes - \(c^{\mathrm{h}}c^{\mathrm{h}}\) for all offspring, Phenotypes - Himalayan for all offspring.

Step by step solution

01

Case 1: Chinchilla x Chinchilla

The phenotype of both rabbits in the P1 generation is chinchilla, which is due to allele \(c^{\mathrm{ch}}\). Since this allele is dominant to all others except \(C\) and they both show the chinchilla phenotype, their genotypes must be \(c^{\mathrm{ch}}c^{\mathrm{ch}}\) for both rabbits. Given this information, both parents will pass on their \(c^{\mathrm{ch}}\) allele to their offspring, and the F1 generation will be entirely comprised of chinchilla offspring with the same \(c^{\mathrm{ch}}c^{\mathrm{ch}}\) genotype.
02

Case 2: Full color x Himalayan

In this case, the phenotype of one parent is full color, and the other parent is Himalayan. The full color phenotype is due to the dominant allele \(C\), while the Himalayan phenotype is due to the \(c^{h}\) allele, which is dominant only to \(c^{a}\). Therefore, the genotypes of the parents must be \(Cc^{\mathrm{h}}\) for the full-color rabbit and \(c^{\mathrm{h}}c^{\mathrm{h}}\) for the Himalayan rabbit. For the F1 generation, the offspring will inherit either \(C\) or \(c^{\mathrm{h}}\) from the full-color parent and will inherit \(c^{\mathrm{h}}\) from the Himalayan parent. This results in F1 offspring with a genotype of \(Cc^{\mathrm{h}}\), which displays a full-color phenotype.
03

Case 3: Himalayan x Himalayan

Here, the phenotype of both rabbits in the P1 generation is Himalayan, which is due to the \(c^{h}\) allele. Since this allele is dominant only to \(c^{a}\) and both parents exhibit the Himalayan phenotype, their genotypes must be \(c^{\mathrm{h}}c^{\mathrm{h}}\) for both rabbits. Given these genotypes, both parents will pass on their \(c^{\mathrm{h}}\) allele to their offspring, and the F1 generation will be comprised entirely of Himalayan offspring with the same \(c^{\mathrm{h}}c^{\mathrm{h}}\) genotype.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Dominance Hierarchy
Genetics often involves understanding how different allele combinations influence the traits of organisms. A key concept in this is the dominance hierarchy of alleles. This hierarchy defines which alleles express their traits over others, forming a ranking order of genetic control. In our rabbit example, **dominance hierarchy** is clearly displayed:
  • The allele \( C \) is the most dominant and always expresses its trait of full coat color, regardless of what other alleles it is paired with.
  • The \( c^{\mathrm{ch}} \) allele, responsible for the chinchilla phenotype, is second in the hierarchy. It shows chinchilla color unless paired with the \( C \) allele.
  • Next is the \( c^{h} \) allele which expresses the Himalayan coat color, but only when \( C \) or \( c^{\mathrm{ch}} \) are not present.
  • The least dominant allele is \( c^{a} \), which results in albino coloration and is only expressed when both copies of the allele are present.
Understanding the dominance hierarchy allows us to predict the phenotypes of offspring given the genotype of parents. It demonstrates that not all alleles contribute equally to an organism's traits.
Coat Color Inheritance
In rabbits, coat color inheritance illustrates how genetic traits are passed from parents to offspring. The color an offspring displays depends on its specific genotype, which it receives through allele combinations from each parent.Each rabbit has two alleles for coat color, one inherited from each parent. The phenotype (visible trait) exhibited by the rabbit is determined by the interaction between these two alleles:
  • If a rabbit inherits at least one \( C \) allele, it will show a full-color coat.
  • If no \( C \) allele is present, but at least one \( c^{\mathrm{ch}} \) allele is inherited, the rabbit will have a chinchilla coat.
  • If the rabbit has no \( C \) or \( c^{\mathrm{ch}} \) alleles, but at least one \( c^{h} \) allele, it will display a Himalayan coat.
  • Finally, if no alleles other than \( c^{a} \) are present, the rabbit will be albino.
This example highlights the importance of **coat color inheritance** in genetic studies, as it provides a straightforward demonstration of how visible characteristics are inherited based on genetic combinations.
Allele Interactions
The way alleles combine and interact within an organism significantly influences its genetic makeup and, consequently, its physical traits. Understanding **allele interactions** allows students to comprehend how various combinations can lead to different phenotypic expressions.In rabbits, certain interactions dominate others based on the presence of more dominant alleles:
  • The \( CC \) genotype results in a full-color coat because \( C \) is the most dominant allele.
  • When \( C \) is absent, \( c^{\mathrm{ch}}c^{\mathrm{ch}} \) leads to a chinchilla coat due to \( c^{\mathrm{ch}} \)'s dominance over \( c^{h} \) and \( c^{a} \).
  • The \( c^{h}c^{h} \) genotype shows the Himalayan pattern in the absence of more dominant alleles.
  • Finally, \( c^{a}c^{a} \) will produce an albino phenotype, as it lacks any dominant alleles to override.
The interaction between these alleles demonstrates how multiple factors work together to determine genetic outcomes. By studying allele interactions, researchers and students can better predict the traits of future generations.

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Most popular questions from this chapter

What is meant by the term epistasis? Distinguish between epis tasis and dominance. Do not use examples in answering this question.

Predict the \(F_{1}\) and \(F_{2}\) results of crossing a male fowl that is cock- feathered with a true-breeding hen-feathered female fowl. Recall that these traits are sex limited.

When summer squash plants (Cucurbita pepo) with discshaped fruits are crossed to ones with long fruits, the \(\mathrm{F}_{1}\) generation all have disc-shaped fruits. When the \(F_{1}\) plants are crossed to each other, the \(\mathrm{F}_{2}\) produce spherical fruits as well as exhibit the two parental strains. The phenotypic ratio is 9: 6: 1 (disc-shaped:spherical:long). (a) Which type of gene interaction is this an example of? (b) Explain the phenotypes observed in terms of the number of gene pairs involved and by designating genotypes for all the fruit shapes in the cross. (Use dashes where required.)

In a unique species of plants, flowers may be yellow, blue, red, or mauve. All colors may be true breeding, If plants with blue flowers are crossed to red- flowered plants, all \(\mathrm{F}_{1}\) plants have yellow flowers. When these produced an \(\mathrm{F}_{2}\) generation, the following ratio was observed: \(9 / 16\) yellow: \(3 / 16\) blue: \(3 / 16\) red: \(1 / 16\) mauve In still another cross using true-breeding parents, yellow-flowered plants are crossed with mauve-flowered plants. Again, all \(\mathrm{F}_{1}\) plants had yellow flowers and the \(\mathrm{F}_{2}\) showed a 9: 3: 3: 1 ratio, as just shown. (a) Describe the inheritance of flower color by defining gene symbols and designating which genotypes give rise to cach of the four phenotypes. (b) Determine the \(F_{1}\) and \(F_{2}\) results of a cross between truebreeding red and true-breeding mauve-flowered plants.

Horses can be cremello (a light cream color), chestnut brownish color), or palomino (a golden color with white in the horse's tail and mane). Of these phenotypes, only palominos never breed true. (a) From the results given above, determine the mode of inheritance by assigning gene symbols and indicating which genotypes yield which phenotypes. (b) Predict the \(F_{1}\) and \(F_{2}\) results of many initial matings between cremello and chestnut horses.
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