Textbook Question
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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14. Genetic Control of Development
Developmental Patterning Genes
2:25 minutesProblem 12
Textbook Question
The homeotic mutation Antennapedia causes mutant Drosophila to have legs in place of antennae and is a dominant gain-of-function mutation. What are the properties of such mutations? How does the Antennapedia gene change antennae into legs?
Verified step by step guidance1
Understand the concept of homeotic mutations: These are mutations in genes that control the development of body structures, causing one body part to develop as another. In this case, the Antennapedia mutation causes legs to form in place of antennae.
Recognize that Antennapedia is a dominant gain-of-function mutation: Gain-of-function mutations result in a gene acquiring a new or enhanced activity. Dominance means that only one copy of the mutated gene is sufficient to cause the phenotype.
Learn about the role of homeotic genes: Homeotic genes, such as Antennapedia, are part of the Hox gene family. These genes encode transcription factors that regulate the expression of other genes, determining the identity of body segments during development.
Explore how the Antennapedia gene functions: In the mutant Drosophila, the Antennapedia gene is misexpressed in the head region where antennae normally develop. This misexpression leads to the activation of leg-specific developmental pathways in the head, replacing antennae with legs.
Understand the mechanism of misexpression: The mutation likely alters the regulatory elements of the Antennapedia gene, causing it to be expressed in the wrong location (the head instead of the thorax). This ectopic expression drives the development of legs in place of antennae.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Homeotic Genes
Homeotic genes are crucial for determining the identity of body segments in organisms. They encode transcription factors that regulate the expression of other genes, guiding the development of specific structures in the correct locations. In Drosophila, mutations in these genes can lead to dramatic changes in morphology, such as the transformation of antennae into legs.
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Segmentation Genes
Gain-of-Function Mutations
Gain-of-function mutations result in a gene product with enhanced or new functions. In the case of the Antennapedia mutation, the altered gene product leads to the inappropriate activation of leg development pathways in the head region, causing legs to form instead of antennae. These mutations can be dominant, meaning that only one copy of the mutated gene is sufficient to produce the phenotype.
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Transcriptional Regulation
Transcriptional regulation involves the control of gene expression at the transcription level, determining when and how much of a gene product is made. In the context of the Antennapedia mutation, the altered regulation allows for the expression of leg-specific genes in the antennae region, effectively reprogramming the developmental fate of those structures. This process is critical for understanding how mutations can lead to significant morphological changes.
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