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Chapter 5: Problem 22

In rabbits, an allelic series helps to determine coat color: \(C\) (full color), \(c^{\mathrm{ch}}\) (chinchilla, gray color), \(c^{\mathrm{h}}\) (Himalayan, white with black extremities), and \(c\) (albino, all-white). The \(C\) allele is dominant to all others, \(c^{\mathrm{ch}}\) is dominant to \(c^{\mathrm{h}}\) and \(c, c^{\mathrm{h}}\) is dominant to \(c\), and \(c\) is recessive to all the other alleles. This dominance hierarchy can be summarized as \(C>c^{\mathrm{ch}}>c^{\mathrm{h}}>c .\) The rabbits in the following list are crossed and produce the progeny shown. Give the genotypes of the parents for each cross: Phenotypes of parents a. full color \(x\) albino b. Himalayan \(\times\) albino c. full color \(\times\) albino d. full color \(x\) Himalayan e. full color \(\times\) full color Phenotypes of offspring \(1 / 2\) full color, \(1 / 2\) albino \(1 / 2\) Himalayan, \(1 / 2\) albino \(1 / 2\) full color, \(1 / 2\) chinchilla \(1 / 2\) full color, \(1 / 4\) Himalayan, \(1 / 4\) albino \(3 / 4\) full color, \(1 / 4\) albino

Short Answer

Expert verified
(a) \( Cc \times cc \); (b) \( c^{h}c \times cc \); (c) \( Cc^{ch} \times cc \); (d) \( Cc^{h} \times c^{h}c \); (e) \( Cc \times Cc \).

Step by step solution

01

Determine Genotypes From Offspring for Cross a

Given the offspring results: 1/2 full color and 1/2 albino, we start by noting the predominance of the full color from the parents. The parents need to be heterozygous for the traits seen in the offspring. Thus, the genotype for the full color parent is \( Cc \) (since 50% full color implies one full-color allele) and the albino parent is \( cc \).
02

Determine Genotypes From Offspring for Cross b

In this cross, outcomes are 1/2 Himalayan and 1/2 albino. The Himalayan parent can only exhibit its phenotype if it has at least one \( c^h \) allele, and the albino offspring indicate a recessive \( c \) allele. Thus, the Himalayan parent's genotype is \( c^h c \) and the albino parent is \( cc \).
03

Determine Genotypes From Offspring for Cross c

The cross results in 1/2 full color and 1/2 chinchilla. The full color here indicates at least one \( C \) allele, while chinchilla signifies a \( c^{ch} \) presence but no full color dominance. Given the offspring, the full color parent is \( Cc^{ch} \) and the albino parent is \( cc \).
04

Determine Genotypes From Offspring for Cross d

Offspring are 1/2 full color, 1/4 Himalayan, and 1/4 albino. The full color offspring suggest a \( C \) dominant allele from full color parent and a variable allele from Himalayan. The full color parent may have other recessive alleles, but offspring do not display shades between \( C \) and albino. Therefore, the full color parent is \( Cc^{h} \) and the Himalayan parent is \( c^{h}c \).
05

Determine Genotypes From Offspring for Cross e

The full color phenotype is 3/4, indicating dominance in full color. However, given that albino appears too, one or both parents must carry the recessive \( c \) allele. Detailing the genotypes, both full color parents must be \( Cc \), allowing for \( CC, Cc, cc \) offspring.

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Key Concepts

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

Alleles
Alleles are different forms of a gene that are found in the same location on a chromosome. They are responsible for the variation in traits or phenotypes that can be observed within a species.
In the context of the rabbit coat color example, alleles determine the color of the rabbit's fur. The notations like \( C \), \( c^\text{ch} \), \( c^\text{h} \), and \( c \) represent different alleles of the coat color gene. Each allele can have a different effect on the rabbit's phenotype.
For example, the \( C \) allele results in a full color coat, \( c^\text{ch} \) results in a chinchilla (gray) coat, \( c^\text{h} \) creates a Himalayan pattern (white with black extremities), and \( c \) leads to an albino coat (all-white). In diploid organisms like rabbits, a pair of alleles (one from each parent) determine the given trait.
Dominance Hierarchy
The concept of dominance hierarchy is crucial in understanding how different alleles interact with each other to produce a phenotype. Dominance hierarchy defines which alleles in a seriel are capable of expressing their traits over others when pairs are present.
In rabbits, the dominance hierarchy is \( C > c^{\mathrm{ch}} > c^{\mathrm{h}} > c \). This means that if a rabbit inherits the \( C \) allele from one parent, the rabbit will exhibit the full coat color, regardless of the second allele.
The dominance order guides us:
  • \( C \) being the strongest, will mask the effects of all other alleles present.
  • \( c^{\mathrm{ch}} \) will be visible only if \( C \) is absent but can still mask \( c^{\mathrm{h}} \) and \( c \).
  • \( c^{\mathrm{h}} \) is expressed only when both \( C \) and \( c^{\mathrm{ch}} \) alleles are absent.
  • \( c \), being recessive, only shows if both alleles in a pair are \( c \).
Mendelian Inheritance
Mendelian inheritance is a set of principles about how traits are passed from parents to offspring through genes, based on Gregor Mendel's work. This inheritance model explains the segregation and assortment of alleles during the formation of gametes.
In Mendelian inheritance, each parent provides one allele for a trait, and the combination of alleles determines the offspring's phenotype. The principles predict that alleles assort independently and segregate into gametes randomly.
For example, in the case of rabbit coat color, Mendel's laws allow us to predict the possible combinations for the offspring based on the known genotypes of the parents. The segregation of alleles during gamete formation results in the phenotypic ratios seen in rabbit offspring.
Rabbit Coat Color
Rabbit coat color is determined by a specific genetic mechanism involving multiple alleles. Each allele can express a different hair pigment, resulting in various color patterns.
In the genetic series given, \( C \) (full color) is dominant, ensuring that any rabbit with at least one \( C \) allele will have full coloration. Other alleles like \( c^{\mathrm{ch}} \) result in chinchilla coloring when \( C \) is absent, while \( c^{\mathrm{h}} \) and \( c \) produce a Himalayan and albino fur, respectively.
Coat color can be complex due to interactions between alleles. Crosses between rabbits can result in patterns dictated by the dominance hierarchy, such as one allele masking another, leading to diversity in rabbit fur.
Genotype Determination
Genotype determination involves understanding which allele combinations are present in an organism and predicting their phenotypic outcomes. Genotypes are written as pairs (e.g., \( CC \), \( Cc \), \( c^{ch}c \), etc.) to denote the alleles inherited from each parent.
Based on offspring phenotypes, it is possible to infer genotypes, which is crucial for solving genetics problems like the ones described. By analyzing the offspring, the possible allele combinations from the parents can be deduced.
For instance, if half of the offspring are albino, it suggests that both parents possessed a \( c \) allele. An understanding of the dominance hierarchy and Mendelian principles aids in accurately determining these genotypic compositions.

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Most popular questions from this chapter

In 1983 , a sheep farmer in Oklahoma noticed in his flock a ram that possessed increased muscle mass in his hindquarters. Many of the offspring of this ram possessed the same trait, which became known as the callipyge phenotype (callipyge is Greek for "beautiful buttocks"). The mutation that caused the callipyge phenotype was eventually mapped to a position on the sheep chromosome 18 . When the male callipyge offspring of the original mutant ram were crossed with normal females, they produced the following progeny: \(1 / 4\) male callipyge, \(1 / 4\) female callipyge, \(1 / 4\) male normal, and \(1 / 4\) female normal. When the female callipyge offspring of the original mutant ram were crossed with normal males, all the offspring were normal. Analysis of the chromosomes of these offspring of callipyge females showed that half of them received a chromosome 18 with the allele encoding callipyge from their mother. Propose an explanation for the inheritance of the allele for callipyge. How might you test your explanation?

A variety of opium poppy (Papaver somniferum) with lacerate leaves was crossed with a variety that has normal leaves. All the \(\mathrm{F}_{1}\) had lacerate leaves. Two \(\mathrm{F}_{1}\) plants were interbred to produce the \(\mathrm{F}_{2} .\) Of the \(\mathrm{F}_{2}, 249\) had lacerate leaves and 16 had normal leaves. Give genotypes for all the plants in the \(\mathrm{P}, \mathrm{F}_{1},\) and \(\mathrm{F}_{2}\) generations. Explain how lacerate leaves are determined in the opium poppy.

Turkeys have black, bronze, or black-bronze plumage. Examine the results of the following crosses: $$ \begin{array}{ll} {\text { Parents }} & {\text { Offspring }} \\ \hline \text { Cross 1: black and bronze } & \text { all black } \\ \text { Cross 2: black and black } & 3 / 4 \text { black, } 1 / 4 \text { bronze } \\ \text { Cross 3: black-bronze and } & \text { all black-bronze } \\ \text { black-bronze } & \\ \text { Cross 4: black and bronze } & 1 / 2 \text { black, } 1 / 4 \text { bronze, } 1 / 4 \\ & \text { black-bronze } \\ \text { Cross 5: bronze and black- } & 1 / 2 \text { bronze, } 1 / 2 \text { black-bronze } \\ \text { bronze } & \\ \text { Cross 6: bronze and bronze } &\\\ &\text {4 bronze,} \text {1 / 4 black-bronze} \end{array} $$ Do you think these differences in plumage arise from incomplete dominance between two alleles at a single locus? If yes, support your conclusion by assigning symbols to each allele and providing genotypes for all turkeys in the crosses. If your answer is no, provide an alternative explanation and assign genotypes to all turkeys in the crosses.

Assume that long ear lobes in humans are an autosomal dominant trait that exhibits \(30 \%\) penetrance. A person who is heterozygous for long ear lobes mates with a person who is homozygous for normal ear lobes. What is the probability that their first child will have long ear lobes?

In chickens, comb shape is determined by alleles at two loci \((R, r\) and \(P, p)\). A walnut comb is produced when at least one dominant allele \(R\) is present at one locus and at least one dominant allele \(P\) is present at a second locus (genotype \(\left.R_{-} P_{-}\right) .\) A rose comb is produced when at least one dominant allele is present at the first locus and two recessive alleles are present at the second locus (genotype \(\left.R_{-} p p\right)\). A pea comb is produced when two recessive alleles are present at the first locus and at least one dominant allele is present at the second (genotype \(r r P_{-}\) ). If two recessive alleles are present at the first and at the second loci \((r r p p)\), a single comb is produced. Progeny with what types of combs and in what proportions will result from the following crosses? a. \(R R \space P P \times \operatorname{rr}\space p p\) b. \(\operatorname{Rr} P p \times \operatorname{rrpp}\) c. \(\operatorname{Rr} P p \times \operatorname{Rr} P p\) d. \(\operatorname{Rr} p p \times \operatorname{Rr} p p\) e. \(\operatorname{Rr} p p \times \operatorname{rr} \mathrm{Pp}\) f. \(\operatorname{Rr} p p \times \operatorname{rrpp}\)
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