Ch. 23 - Developmental Genetics

Klug - Concepts of Genetics 12th Edition

Klug12th EditionConcepts of GeneticsISBN: 9780135564776당신이 사용하는 게 아니라요?교과서 변경

Klug 12th Edition

Ch. 23 - Developmental Genetics

문제 12

23장, 문제 12

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?

검증된 단계별 안내

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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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.

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.

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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교과서 질문

Embryogenesis and oncogenesis (generation of cancer) share a number of features including cell proliferation, apoptosis, cell migration and invasion, formation of new blood vessels, and differential gene activity. Embryonic cells are relatively undifferentiated, and cancer cells appear to be undifferentiated or dedifferentiated. Homeotic gene expression directs early development, and mutant expression leads to loss of the differentiated state or an alternative cell identity. M. T. Lewis [(2000). Breast Can. Res. 2:158–169] suggested that breast cancer may be caused by the altered expression of homeotic genes. When he examined 11 such genes in cancers, 8 were underexpressed while 3 were overexpressed compared with controls. Given what you know about homeotic genes, could they be involved in oncogenesis?

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교과서 질문

Experiments have shown that any nuclei placed in the polar cytoplasm at the posterior pole of the Drosophila egg will differentiate into germ cells. If polar cytoplasm is transplanted into the anterior end of the egg just after fertilization, what will happen to nuclei that migrate into this cytoplasm at the anterior pole?

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교과서 질문

You observe that a particular gene is being transcribed during development. How can you tell whether the expression of this gene is under transcriptional or translational control?

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교과서 질문

Early development depends on the temporal and spatial interplay between maternally supplied material and mRNA and the onset of zygotic gene expression. Maternally encoded mRNAs must be produced, positioned, and degraded [Surdej and Jacobs-Lorena (1998). Mol. Cell Biol. 18:2892–2900]. For example, transcription of the bicoid gene that determines anterior–posterior polarity in Drosophila is maternal. The mRNA is synthesized in the ovary by nurse cells and then transported to the oocyte, where it localizes to the anterior ends of oocytes. After egg deposition, bicoid mRNA is translated and unstable bicoid protein forms a decreasing concentration gradient from the anterior end of the embryo. At the start of gastrulation, bicoid mRNA has been degraded. Consider two models to explain the degradation of bicoid mRNA: (1) degradation may result from signals within the mRNA (intrinsic model), or (2) degradation may result from the mRNA's position within the egg (extrinsic model). Experimentally, how could one distinguish between these two models?

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교과서 질문

How can you determine whether a particular gene is being transcribed in different cell types?

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교과서 질문

The Drosophila homeotic mutation spineless aristapedia (ssᵃ) results in the formation of a miniature tarsal structure (normally part of the leg) on the end of the antenna. What insight is provided by (ssᵃ) concerning the role of genes during determination?

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