DEVELOPMENT QUESTION 1988:				L. PETERSON/AP BIOLOGY
	Discuss the processes of cleavage, gastrulation, and neurulation in the frog 
	embryo; tell what each process accomplishes.
	Describe an experiment that illustrates the importance of induction in 
	development.
  
  STANDARDS:
          1 point for each major item under each major heading
  CLEAVAGE          (max. 3 points)
  __Mitotic or cell division, or increase in cell number
  __No cellular growth
  __Holoblastic (complete division)
  __Unequal
  __Radial (Indeterminant)
  __Involves use of maternal RNA
  
  __1st vertical              [1 point for directionality of early cleavage divisions]
  __2nd vertical, perpendicular to 1st
  __3rd horizontal, perpendicular to 1st and 2nd, unequal
  __Grey crescent establishes planes of cleavage
  
  __Divisions more rapid at animal pole                     (max. 2 points)
  
     Accomplishes
  __Forms blastula or hollow ball of cells
  __Forms blastocoel
  __Forms blastomeres (micromeres, macromeres)
  __Forms or increases DNA in embryo
  __Produces unequal distribution of cytoplasmic contents in blastomeres(max. 2 points)
   
  NEURULATION  (max. 3 points)
  __Epidermal thickening, flattening in dorsal midline (neural plate formation)
  __Plate develops longitudinal depression (neural groove, neural folds)
  __Neural folds fuse
  __Neural tube pinches free of epidermis, sinks inward               
  __Notochord (chordamesoderm) required for neurulation          (max. 2 points)
  
     Accomplishes
  __Forms neural tube (CNS, nerve cord, spinal cord, brain, nervous system)
  __Forms neurula
  __Forms neural crests                                (max. 2 points)
  
  
  GASTRULATION      (max. 3 points)
  __Formation of yolk plug
  __Formation of blastopore
  __Invagination ("folds in", "pushes in")
  __Involution
  __Epiboly/cell migration
  __Proliferation/movement forward of notochordal tissue internally from blastopore.
          (chordamesoderm, primary mesoderm)
  __Forward movement of mesodermal wings internally from blastopore.
          (lateral plate mesoderm, somitic mesoderm)
                                                  (max. 2 points)
  
     Accomplishes
  __Establishes germ layers or triploblastic embryo;
         ecto-, meso-, endo- (or ento-)derm     (must mention 2)
  __Forms gastrula
  __Establishes embryonic axes
  __Forms gastrocoel (archenteron, gut or digestive system)
  __Internalizes yolk
  __Obliterates blastocoel
  __Moves cells to sites where poised for organogenesis               (max. 2 points)
  
  INDUCTION EXPERIMENT   (max. 3 points)
  In the context of an experiment, description of:
        What induction is:
          Cells [or products] influence neighboring cells
  
        What induction does:
          Changes gene expression
          Induces differentiation
          Alters subsequent development
  
         Inducing Tissue (organizer)
         Induced Tissue and what it forms
  
  Examples:
  __Dorsal lip of blastopore --- induces gastrulation or neurulation of "belly" ectoderm
  __Optic vesicle --- induces lens formation in epidermal ectoderm
  __Notochord --- induces neurulation of neural ectoderm