Textbook Question
Why do loss-of-function mutations in Hox genes usually result in embryo lethality, whereas gain-of-function mutants can be viable? Why are flies homozygous for the recessive loss-of-function alleles and viable?
Ch. 18 - Developmental Genetics
Sanders3rd EditionGenetic Analysis: An Integrated ApproachISBN: 9780135564172
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Table of contents
- Ch. 1 - The Molecular Basis of Heredity, Variation, and Evolution64
- Ch. 2 - Transmission Genetics144
- Ch. 3 - Cell Division and Chromosome Heredity81
- Ch. 4 - Gene Interaction87
- Ch. 5 - Genetic Linkage and Mapping in Eukaryotes103
- Ch. 6 - Genetic Analysis and Mapping in Bacteria and Bacteriophages73
- Ch. 7 - DNA Structure and Replication71
- Ch. 8 - Molecular Biology of Transcription and RNA Processing79
- Ch. 9 - The Molecular Biology of Translation110
- Ch. 10 - Eukaryotic Chromosome Abnormalities and Molecular Organization100
- Ch. 11 - Gene Mutation, DNA Repair, and Homologous Recombination86
- Ch. 12 - Regulation of Gene Expression in Bacteria and Bacteriophage90
- Ch. 13 - Regulation of Gene Expression in Eukaryotes38
- Ch. 14 - Analysis of Gene Function via Forward Genetics and Reverse Genetics72
- Ch. 15 - Recombinant DNA Technology and Its Applications69
- Ch. 16 - Genomics: Genetics from a Whole-Genome Perspective49
- Ch. 17 - Organelle Inheritance and the Evolution of Organelle Genomes27
- Ch. 18 - Developmental Genetics43
- Ch. 19 - Genetic Analysis of Quantitative Traits66
- Ch. 20 - Population Genetics and Evolution at the Population, Species, and Molecular Levels105
Sanders3rd EditionGenetic Analysis: An Integrated ApproachISBN: 9780135564172Not the one you use?Change textbook
Chapter 18, Problem 8
Compare and contrast the specification of segmental identity in Drosophila with that of floral organ specification in Arabidopsis. What is the same in this process, and what is different?
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Step 1: Understand the concept of segmental identity in Drosophila. Segmental identity in Drosophila is determined by a group of genes known as Hox genes. These genes are responsible for the development of specific body segments and ensure that each segment develops the appropriate structures.
Step 2: Explore the role of Hox genes in Drosophila. Hox genes are expressed in specific patterns along the anterior-posterior axis of the embryo, and their expression is regulated by a hierarchy of gene interactions, including gap genes, pair-rule genes, and segment polarity genes.
Step 3: Learn about floral organ specification in Arabidopsis. In Arabidopsis, floral organ identity is specified by the ABC model, which involves three classes of genes (A, B, and C) that interact to determine the identity of the floral organs: sepals, petals, stamens, and carpels.
Step 4: Compare the genetic mechanisms. Both Drosophila and Arabidopsis use a combinatorial code of gene expression to specify identity, but the specific genes and their interactions differ. In Drosophila, Hox genes are key, while in Arabidopsis, the ABC model genes play a central role.
Step 5: Contrast the developmental contexts. Drosophila segmental identity involves the development of body segments in an animal, while Arabidopsis floral organ specification involves the development of flower parts in a plant. Despite these differences, both processes illustrate how specific gene expression patterns can lead to the development of distinct structures.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Segmental Identity in Drosophila
In Drosophila, segmental identity is determined by a series of genes known as segmentation genes, which include gap, pair-rule, and segment polarity genes. These genes establish the anterior-posterior axis and define the identity of each segment through a cascade of regulatory interactions. The homeotic genes then specify the characteristics of each segment, ensuring that body parts develop in the correct locations.
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Segmentation Genes
Floral Organ Specification in Arabidopsis
In Arabidopsis, floral organ specification is governed by the ABC model of flower development, which involves three classes of genes (A, B, and C) that interact to determine the identity of floral organs. Class A genes specify sepals, A and B together specify petals, B and C specify stamens, and C alone specifies carpels. This model illustrates how specific gene interactions lead to the formation of distinct floral structures.
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Comparative Developmental Genetics
Comparative developmental genetics examines how different organisms use similar genetic mechanisms to achieve diverse developmental outcomes. In both Drosophila and Arabidopsis, gene regulatory networks play a crucial role in determining body and organ identity. While the specific genes and their interactions differ, the underlying principles of spatial and temporal gene expression are fundamental to both processes, highlighting evolutionary conservation in developmental biology.
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Related Practice
Textbook Question
Actinomycin D is a drug that inhibits the activity of RNA polymerase II. In the presence of actinomycin D, early development in many vertebrate species, such as frogs, can proceed past the formation of a blastula, a hollow ball of cells that forms after early cleavage divisions, but development ceases before gastrulation (the stage at which cell layers are established). What does this tell you about maternal versus zygotic gene activity in early frog development?
Textbook Question
What is the difference between a parasegment and a segment in Drosophila development? Why do developmental biologists think of parasegments as the subdivisions that are produced during the development of flies?
Textbook Question
Consider the even-skipped regulatory sequences in Figure 18.9.
Explain what you expect to see happen to even-skipped stripe 2 if it is expressed in a Krüppel mutant background. What about a hunchback mutant background? A giant mutant background? A bicoid mutant background?
Textbook Question
Ablation of the anchor cell in wild-type C. elegans results in a vulva-less phenotype.
What about if the anchor cell is ablated in a let-23 gain-of-function mutant?
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Textbook Question
Ablation of the anchor cell in wild-type C. elegans results in a vulva-less phenotype.
What phenotype is to be expected if the anchor cell is ablated in a let-23 loss-of-function mutant?