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 \(C>c^{\kappa h}>c^{h}>c^{a} \cdot\) For each of the following three cases, the phenotypes of the \(P_{1}\) generations of two crosses are shown, as well as the phenotype of one member of the \(F_{1}\) generation.

Short Answer

Expert verified
Answer: The process to determine the possible genotypes of rabbits in the given cross involves three steps: 1. Determine the phenotypes of each rabbit in the P1 and F1 generations. 2. Identify possible genotypes of the rabbits using the phenotypes and the order of dominance. 3. Determine which of the possible genotypes are compatible with the given cross.

Step by step solution

01

Determine phenotypes of each rabbit

For this case, first identify the phenotype of each rabbit given in the \(P_{1}\) generation and the single \(F_{1}\) generation member.
02

Identify possible genotypes of the rabbits

Using the phenotypes of each rabbit, along with the order of dominance, infer the possible genotypes of the rabbits in the \(P_{1}\) and \(F_{1}\) generations.
03

Determine which of the possible genotypes are compatible with the given cross

Analyze the potential genotypes of the three rabbits and see which combinations are consistent with the offspring produced by the given cross. Repeat these steps for cases 2 and 3. #Case 2#
04

Determine phenotypes of each rabbit

For this case, first identify the phenotype of each rabbit given in the \(P_{1}\) generation and the single \(F_{1}\) generation member.
05

Identify possible genotypes of the rabbits

Using the phenotypes of each rabbit, along with the order of dominance, infer the possible genotypes of the rabbits in the \(P_{1}\) and \(F_{1}\) generations.
06

Determine which of the possible genotypes are compatible with the given cross

Analyze the potential genotypes of the three rabbits and see which combinations are consistent with the offspring produced by the given cross. #Case 3#
07

Determine phenotypes of each rabbit

For this case, first identify the phenotype of each rabbit given in the \(P_{1}\) generation and the single \(F_{1}\) generation member.
08

Identify possible genotypes of the rabbits

Using the phenotypes of each rabbit, along with the order of dominance, infer the possible genotypes of the rabbits in the \(P_{1}\) and \(F_{1}\) generations.
09

Determine which of the possible genotypes are compatible with the given cross

Analyze the potential genotypes of the three rabbits and see which combinations are consistent with the offspring produced by the given cross.

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Key Concepts

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

Genetic Dominance
In understanding the concept of genetic dominance, envision a hierarchy of traits within an organism that determine how certain characteristics are expressed. Dominant alleles are akin to a 'boss' in this hierarchy and tend to mask the presence of other alleles, known as recessive alleles, when an individual is heterozygous (possesses different alleles) for a particular gene.

In the rabbit coat color example, the allele represented by the symbol C overshadows the effects of the other alleles and results in a fully colored coat when present. Such dominant-recessive relationships are foundational in predicting the outcome of genetic crosses. These predictions are made simpler by using symbols to represent dominance: uppercase letters for dominant alleles and lowercase for recessive ones. This symbolic system is handy when determining which traits will appear in offspring, known as phenotypes.
Mendelian Genetics
Named after the pioneering work of Gregor Mendel, Mendelian genetics provides the basic principles of heredity through simple rules. Mendel's first law, the Law of Segregation, states that an organism has two alleles for each inherited trait, and these alleles separate during the formation of gametes (egg and sperm). Each gamete carries only one allele for each trait.

Mendel's second law, the Law of Independent Assortment, tells us that genes for different traits are passed independently of one another from parents to offspring. Though Mendelian genetics generally deals with single-gene traits, the concept still holds invaluable ground when discussing multiple alleles inheritance, as is the case with rabbit coat colors. Each rabbit carries two alleles for coat color, and through Mendel's laws, the distribution of these alleles can be predicted in the offspring.
Allele Interactions
Allele interactions go beyond the basic dominant and recessive patterns to explain more complex inheritance scenarios. With multiple alleles, like in our rabbit coat color example, there can be several variants of a gene within a population. The interaction of these alleles is critical as it determines the phenotypic expression. In the rabbits' case, we see this interaction as a hierarchy, where allele C is dominant over cch, ch, and ca, with each subsequent allele dominating the one following it.

Incomplete Dominance and Codominance

In some cases, alleles will exhibit incomplete dominance, where the heterozygous phenotype is a blend of the two alleles, or codominance, where both alleles in the heterozygous state are fully expressed. These patterns add additional layers to genetic prediction and enhance our understanding of genetic diversity.
Phenotype and Genotype Analysis
Phenotype refers to the observable traits of an organism, such as the coat color in rabbits, while genotype refers to the specific alleles an organism carries. Analyzing phenotypes and genotypes is fundamental in genetics for uncovering the heredity patterns of organisms.

To analyze genotypes, one must consider both the potential allele combinations an individual might have and the patterns of inheritance that govern them. For example, as seen in the rabbit exercise, through understanding the phenotype and the order of dominance, we can infer possible genotypes for each rabbit. The genotype analysis is a detective work that involves hypothesis testing and probability assessment to predict the genotypic and phenotypic makeup of future generations. This examination is quintessential for genetic research, breeding programs, and understanding health implications related to genetics.

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Most popular questions from this chapter

A true-breeding purple-leafed plant isolated from one side of El Yunque, the rain forest in Puerto Rico, was crossed to a truebreeding white variety found on the other side. The \(\mathrm{F}_{1}\) offspring were all purple. A large number of \(\mathrm{F}_{1} \times \mathrm{F}_{1}\) crosses produced the following results: \\[ \text { purple: } 4219 \quad \text { white: } 5781 \quad(\text { Total }=10,000) \\] Propose an explanation for the inheritance of leaf color. As a geneticist, how might you go about testing your hypothesis? Describe the genetic experiments that you would conduct.

Discuss the topic of phenotypic expression and the many factors that impinge on it.

In Shorthorn cattle, coat color may be red, white, or roan. Roan is an intermediate phenotype expressed as a mixture of red and white hairs. The following data are obtained from various crosses: red \(\times\) red \(\longrightarrow\) all red white \(\times\) white \(\longrightarrow\) all white red \(\times\) white \(\longrightarrow\) all roan \\[\text { roan } \times \operatorname{roan} \longrightarrow 1 / 4 \text { red: } 1 / 2\\] roan: \(1 / 4\) white (a) How is coat color inherited? What are the genotypes of parents and offspring for each cross? (b) Does the roan phenotype illustrate a case of incomplete dominance or a case of codominance? Explain.

In Drosophila , the X-linked recessive mutation vermilion (v) causes bright red eyes, in contrast to the brick-red eyes of wild type. A separate autosomal recessive mutation, suppressor of vermilion \((s u-v),\) causes flies homozygous or hemizygous for \(v\) to have wildtype eyes. In the absence of vermilion alleles, su-v has no effect on eye color. Determine the \(F_{1}\) and \(F_{2}\) phenotypic ratios from a cross between a female with wild-type alleles at the vermilion locus, but who is homozygous for \(s u\) -v, with a vermilion male who has wildtype alleles at the su-v locus.

In mice, a short-tailed mutant was discovered. When it was crossed to a normal long-tailed mouse, 4 offspring were short-tailed and 3 were long-tailed. Two short-tailed mice from the \(\mathrm{F}_{1}\) generation were selected and crossed. They produced 6 short-tailed and 3 long-tailed mice. These genetic experiments were repeated three times with approximately the same results. What genetic ratios are illustrated? Hypothesize the mode of inheritance and diagram the crosses.

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