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BIO310: Developmental Biology

Unit 3: Cleavage   Now that the egg is fertilized, it must still develop from a single cell into a multicellular organism.  The first step in this process is extremely rapid cleavage; during this time, the egg undergoes a tremendous amount of cell division without increasing in overall size.  All embryos undergo this stage of development, but different types of embryos exhibit very different kinds of cleavage patterns.
 
Also, beginning during cleavage (although this is a process that can continue during much of development), cells’ fates begin to be “specified”—that is, they are committed to forming a particular type of tissue or structure different from other structures.  Specification is the first step in the differentiation process that ends with determination, at which point cells’ fates are fixed and cannot be altered based on outside or surrounding influences.

Unit3 Learning Outcomes
Upon successful completion of this unit, students will be able to:

  • Distinguish between types of cleavage and identify which groups of organisms undergo which type of cleavage.
  • Understand the steps of the cleavage process and what effect the presence or absence of specific molecules and structures have on that process.
  • Distinguish between “specification” and “differentiation” and various types of specification.

3.1 Mechanisms of Cleavage   - Reading: The National Institutes of Health: Professor Scott Gilbert’s Developmental Biology: “An Introduction to Early Development” Link: The National Institutes of Health: Professor Scott Gilbert’s Developmental Biology: “An Introduction to Early Development” (HTML)
 
Instructions: Read the entirety of the subsection on “Cleavage” along with all associated figures (Figs. 8.1-8.5). This will cover the material in 3.1-3.4.
 
Terms of Use: Please respect the copyright and terms of use displayed on the webpage above.

3.1.1 Mitosis Promoting Factor (MPF)   3.1.2 Mechanisms of Mitosis   3.2 Cleavage Patterns   3.2.1 Poles   3.2.2 Yolk   3.3 Holoblastic Cleavage: Isolecithal and Mesolecithal   3.3.1 Bilateral   3.3.2 Spiral   3.3.3 Radial   3.3.3.1 Isolecithal   3.3.3.2 Mesolecithal   3.3.4 Rotational   3.4 Meroblastic Cleavage: Telolecithal and Centrolecithal   3.4.1 Bilateral   3.4.2 Discoidal   3.4.3 Superficial   3.5 Cleavage Patterns in Major Groups of Organisms   3.5.1 Sea Urchins   - Reading: The National Institutes of Health: Professor Scott Gilbert’s Developmental Biology: “The Early Development of Sea Urchins” Link: The National Institutes of Health: Professor Scott Gilbert’s Developmental Biology: “The Early Development of Sea Urchins” (HTML)
 
Instructions: Read all of the subsection on “Cleavage,” along with associated figures (Figs. 8.8-8.14), except for the portion on “Axis Specification.”
 
Terms of Use: Please respect the copyright and terms of use displayed on the webpage above.

3.5.2 Amphibians   - Reading: The National Institutes of Health: Professor Scott Gilbert’s Developmental Biology: “Early Amphibian Development” Link: The National Institutes of Health: Professor Scott Gilbert’s Developmental Biology: “Early Amphibian Development” (HTML)
 
Instructions: Read all of the subsection on “Cleavage,” along with associated figures (Figs. 10.1-10.4).
 
Terms of Use: Please respect the copyright and terms of use displayed on the webpage above.

3.5.3 Birds   - Reading: The National Institutes of Health: Professor Scott Gilbert’s Developmental Biology: “Early Development in Birds” Link: The National Institutes of Health: Professor Scott Gilbert’s Developmental Biology: “Early Development in Birds” (HTML)
 
Instructions: Read all of the subsection on “Cleavage,” along with associated figures (Figs. 11.8-11.9).
 
Terms of Use: Please respect the copyright and terms of use displayed on the webpage above.

3.5.4 Mammals   - Reading: The National Institutes of Health: Professor Scott Gilbert’s Developmental Biology: “Early Mammalian Development” Link: The National Institutes of Health: Professor Scott Gilbert’s Developmental Biology: “Early Mammalian Development” (HTML)
 
Instructions: Read all of the subsection on “Cleavage,” along with associated figures (Figs. 11.20-11.25).
 
Terms of Use: Please respect the copyright and terms of use displayed on the webpage above.

3.6 Cell Specification   - Reading: The National Institutes of Health: Professor Scott Gilbert’s Developmental Biology: “The Developmental Mechanics of Cell Specification” Link: The National Institutes of Health: Professor Scott Gilbert’s Developmental Biology: “The Developmental Mechanics of Cell Specification” (HTML)
 
Instructions: Read this section in its entirety along with all associated figures (Figs. 3.7-3.25). This will cover the material in 3.6.
 
Terms of Use: Please respect the copyright and terms of use displayed on the webpage above.

3.6.1 Specification vs. Determination   3.6.2 Autonomous Specification   3.6.3 Conditional Specification   3.6.4 Syncytial Specification