Table of contents

1. Introduction to Genetics51m
2. Mendel's Laws of Inheritance3h 37m
3. Extensions to Mendelian Inheritance2h 41m
4. Genetic Mapping and Linkage2h 28m
5. Genetics of Bacteria and Viruses1h 21m
6. Chromosomal Variation1h 48m
7. DNA and Chromosome Structure56m
8. DNA Replication1h 10m
9. Mitosis and Meiosis1h 34m
10. Transcription1h 0m
11. Translation58m
12. Gene Regulation in Prokaryotes1h 19m
13. Gene Regulation in Eukaryotes44m
14. Genetic Control of Development44m
15. Genomes and Genomics1h 50m
16. Transposable Elements47m
17. Mutation, Repair, and Recombination1h 6m
18. Molecular Genetic Tools19m
- Genetic Cloning
  9m
- Methods for Analyzing DNA
  9m
19. Cancer Genetics29m
- Overview of Cancer
  21m
- Cancer Mutations
  7m
20. Quantitative Genetics1h 26m
21. Population Genetics50m
- Hardy Weinberg
  19m
- Allelic Frequency Changes
  31m
22. Evolutionary Genetics29m

14. Genetic Control of Development

Developmental Patterning Genes

Genetics

14. Genetic Control of Development

Developmental Patterning Genes

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2:38 minutes

Problem 4b

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?

Verified step by step guidance

Understand the key difference between Drosophila development and other animal species' development: Drosophila development occurs in a syncytial blastoderm, where nuclei share a common cytoplasm, allowing transcription factors to diffuse freely. In contrast, other species undergo cellular cleavage, where individual cells are formed, and transcription factors are restricted to their respective cells.

Recognize that in a syncytial blastoderm, the model assumes that transcription factors can freely diffuse and establish gradients across the shared cytoplasm. This allows for the formation of positional information based on these gradients.

For species with cellular cleavage, the model must account for the fact that transcription factors are confined within individual cells. This means that diffusion between cells is not possible, and positional information must be established through mechanisms such as cell signaling or localized transcription factor production.

Incorporate mechanisms like cell-cell communication (e.g., signaling pathways such as Notch, Wnt, or Hedgehog) into the model to explain how cells coordinate their development in the absence of a shared cytoplasm.

Adjust the model to include the role of cell membranes as barriers to diffusion and emphasize the importance of localized gene expression and intercellular signaling in establishing developmental patterns in species with cellular cleavage.

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Key Concepts

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

Syncytial Blastoderm

A syncytial blastoderm is a stage in early embryonic development where multiple nuclei share a common cytoplasm without cellular boundaries. In Drosophila, this allows for the free diffusion of transcription factors, facilitating coordinated gene expression across the embryo. Understanding this concept is crucial for comparing it to other developmental models where individual cells are formed early on.

Cellular Cleavage

Cellular cleavage refers to the series of rapid mitotic divisions that occur after fertilization, resulting in the formation of smaller cells called blastomeres. In many animal species, this process leads to a multicellular embryo from the outset, contrasting with the syncytial development seen in Drosophila. Recognizing how cleavage patterns influence development is essential for modifying models to fit non-syncytial organisms.

Transcription Factors

Transcription factors are proteins that regulate the expression of specific genes by binding to nearby DNA. In the context of early development, they play a critical role in determining cell fate and pattern formation. In a syncytial environment, these factors can diffuse freely, while in cellular cleavage models, their distribution and activity must be tightly regulated within individual cells, necessitating adjustments to developmental models.

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Multiple Choice

Which of the following HOX clusters are responsible for forming the abdominal in Drosophila development?

In Arabidopsis, which class of HOX genes are responsible for forming the plant carpels?

In the discussion, we have focused on large-scale as well as the inter- and intracellular events that take place during embryogenesis and the formation of adult structures. In particular, we discussed how the adult body plan is laid down by a cascade of gene expression, and the role of cell–cell communication in development. Based on your knowledge of these topics, answer several fundamental questions:

How do we know that eye formation in all animals is controlled by a binary switch gene?

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Textbook Question

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

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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

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?

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Textbook Question

Consider the even-skipped regulatory sequences in Figure 18.9.

Consider the binding sites for gap proteins and Bicoid in the stripe 2 enhancer module. What sites are occupied in parasegments 2, 3, and 4, and how does this result in expression or no expression?

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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?

384

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