Chapter 17

Summary		Questions		Media Resources
17.1 Development is a regulated process.
• Vertebrate development is initiated by a rapid cleavage of the fertilized egg into a hollow ball of cells, the blastula. Cell movements then form primary germ layers and organize the structure of the embryo. • Cells determined in the insect embryo are carried within the body of larvae as imaginal discs, which are assembled into the adult body during pupation. • Plant meristems continuously produce new tissues, which then differentiate into body parts. This differentiation is significantly influenced by the environment.		1. What is cleavage? How does the type of cleavage influence subsequent embryonic development? 2. What is a blastula? How does it form and what does it turn into? 3. What is a gastrula? Where are the germ layers in a gastrula? 4. What is neurulation? How and when does it occur?		•Introduction to Development
17.2 Multicellular organisms employ the same basic mechanisms of development.
• Cell movement in animal development is carried out by altering a cell's complement of surface adhesion molecules, which it uses to pull itself over other cells. • A key to animal development is the ability of cells to alter the developmental paths of adjacent cells, a process called induction. Induction is achieved by diffusible chemicals called morphogens. • Determination of a cell's ultimate developmental fate often involves the addition to it of positional labels that reflect its location in the embryo. • The location of structures within body segments is dictated by a spatially organized assembly of homeotic genes, first discovered in Drosophila but now known to occur in all animals. • Many cells are genetically programmed to die, usually soon after they are formed during development, in a process called apoptosis.		5. What role do cadherins and integrins play in cell movement? 6. What is the difference between mosaic development and regulative development? 7. How do organizers and morphogens participate in induction? 8. How is determination distinguished from differentiation? 9. What role does maternal mRNA play in the development of a Drosophila embryo? 10. What are homeotic genes and what do they do?		•Induction •Pattern Formation • Vertebrate Limb Formation • Homeobox Genes in the Medicinal Leech •Cloning Experiment
17.3 Four model developmental systems have been extensively researched.
• The four most intensively studied model systems of development are the mouse Mus musculus, the fruit fly Drosophila melanogaster, the nematode Caenorhabditis elegans, and the flowering plant Arabidopsis thaliana.		11.  What are the major differences between vertebrate, insect, and plant developmental pathways? What are the similarities?
17.4 Aging can be considered a developmental process.
• Aging is not well understood, although not for want of theories, most of which involve progressive damage to DNA.		12.  Cancer cell cultures never seem to grow old, dividing ceaselessly. What can you deduce about the state of their telomerase gene?		•Unraveling the Mystery of Aging • I'm Not Dead Yet

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