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Ch. 18 - Developmental Genetics
Sanders - Genetic Analysis: An Integrated Approach 3rd Edition
Sanders3rd EditionGenetic Analysis: An Integrated ApproachISBN: 9780135564172Not the one you use?Change textbook
All textbooksSanders 3rd EditionCh. 18 - Developmental GeneticsProblem 3
Chapter 18, Problem 3

How is positional information provided along the anterior–posterior axis in Drosophila? What are the functions of bicoid and nanos?

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span>1. Understand the concept of positional information in Drosophila: Positional information refers to the spatial cues that help cells determine their location within an organism, guiding their development into specific structures. In Drosophila, this is crucial for establishing the anterior-posterior (head-to-tail) axis during embryogenesis.
span>2. Learn about maternal effect genes: These are genes whose products are deposited in the egg by the mother and are essential for early development. In Drosophila, two key maternal effect genes are bicoid and nanos, which play critical roles in establishing the anterior-posterior axis.
span>3. Explore the role of bicoid: Bicoid is a maternal effect gene that encodes a protein acting as a morphogen. It is deposited in the anterior part of the egg and forms a concentration gradient. High concentrations of bicoid protein at the anterior end activate genes necessary for head and thorax development.
span>4. Examine the function of nanos: Nanos is another maternal effect gene, but it is involved in posterior development. It is localized at the posterior end of the egg and inhibits the translation of hunchback mRNA, a gene that would otherwise promote anterior structures. This inhibition allows for the proper development of posterior structures.
span>5. Integrate the roles of bicoid and nanos: Together, bicoid and nanos establish a gradient of positional information along the anterior-posterior axis. Bicoid promotes anterior development, while nanos ensures posterior development by regulating the expression of other genes, thus providing a blueprint for the embryo's body plan.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Positional Information in Development

Positional information refers to the spatial cues that guide the development of an organism, particularly during embryogenesis. In Drosophila, this information is crucial for establishing the anterior-posterior axis, which determines the head-to-tail orientation of the embryo. It is provided by gradients of specific morphogens that influence gene expression and cell fate.
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Bicoid Protein

Bicoid is a key morphogen in Drosophila that is essential for anterior development. It is produced at the anterior end of the embryo and forms a concentration gradient, with higher levels at the front. Bicoid activates the expression of target genes that promote the formation of head structures, thus playing a critical role in establishing the anterior-posterior axis.
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Nanos Protein

Nanos is another important morphogen that functions primarily at the posterior end of the Drosophila embryo. It inhibits the translation of specific mRNAs, thereby regulating the development of posterior structures. Nanos works in conjunction with Bicoid to create a balance of positional information, ensuring proper segmentation and differentiation along the anterior-posterior axis.
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Related Practice
Textbook Question

Explain why many developmental genes encode either transcription factors or signaling molecules.

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Textbook Question

Bird beaks develop from an embryonic group of cells called neural crest cells that are part of the neural tube, which gives rise to the spinal column and related structures. Amazingly, neural crest cells can be surgically transplanted from one embryo to another, even between embryos of different species. When quail neural crest cells were transplanted into duck embryos, the beak of the host embryo developed into a shape similar to that found in quails, creating the 'quck.' Duck cells were recruited in addition to the quail cells to form part of the quck beak. Conversely, when duck neural crest cells were transplanted into quail embryos, the beak of the embryo resembled that of a duck, creating a 'duail,' and quail cells were recruited to form part of the beak. What do these experiments tell you about the autonomy or nonautonomy of the transplanted and host cells during beak development?

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Textbook Question

Early development in Drosophila is atypical in that pattern formation takes place in a syncytial blastoderm, allowing free diffusion of transcription factors between nuclei. In many other animal species, the fertilized egg is divided by cellular cleavages into a larger and larger number of smaller and smaller cells.

What constraints does the formation of a syncytial blastoderm impose on the mechanisms of pattern formation?

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Textbook Question

Early development in Drosophila is atypical in that pattern formation takes place in a syncytial blastoderm, allowing free diffusion of transcription factors between nuclei. In many other animal species, the fertilized egg is divided by cellular cleavages into a larger and larger number of smaller and smaller cells.

How must the model that describes Drosophila development be modified for describing animal species whose early development is not syncytial?

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Textbook Question

Consider the even-skipped regulatory sequences in the following figure:

How are the sharp boundaries of expression of Eve Stripe 2 formed?

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