Zoology 433                                                             Name: _______________________

Midterm 2    March 5, 2004


1.  Fill in the blank (12 points)

What point in early embryogenesis of sea urchins or amphibians do each of the following events occur? 

Possible answers include:               Fertilization

                                                            Cleavage stage

                                                            Midblastula transition



  1. Cell division without growth  ________________________
  2. Onset of large scale embryonic gene transcription           _________________
  3. Blastocoel formation _____________________
  4. Inclusion of G1 and G2 phases in the cell cycle     ____________________
  5. Generation of the primary germ layers       ______________________
  6. Switch from maternal to embryonic control of embryogenesis  __________________


2.  Multiple choice  (20 points)                (circle all of the right answers!)


A. Oncogenes arise from proto-oncogenes by

  1. gain-of-function mutations.
  2.  loss-of-function mutations.
  3. dominant-negative mutations
  4. DNA virus replication


B. Tumor Suppressor genes normally function to :

  1. promote the cell cycle.
  2. inhibit the cell cycle.
  3. promote apoptosis.
  4. inhibit apoptosis.


C.  In a mammalian embryo, epiblast gives rise to

a.      Trophoblast

b.      Endoderm

c.      Mesoderm

d.      Ectoderm

e.      Echinoderm


D.  The archenteron is lined with

  1. Trophoblast
  2. Endoderm
  3. Ectoderm
  4. Mesoderm
  5. Echinoderm


E.  The following events characterize mammalian development, but NOT chick development


a.      compaction at the 8-cell stage

b.      asynchronous cleavage

c.      discoidal cleavage

d.      formation of the primitive streak (or primitive groove)

e.      implantation


3.  Cortical rotation (10 points)

Describe cortical rotation in an amphibian egg as follows:

  1. What developmental or cellular event causes in cortical rotation?





  1. What rotates?  Explain in complete sentences.






  1. Describe how cortical rotation influences b-catenin location or activity. 

4.  Dorsal blastopore lip (10 points)

Spemann and Mangold grafted the dorsal blastopore lip of an early amphibian gastrula onto the ventral side of a host early gastrula.  


a)   Did this change the fate of the grafted tissue (the dorsal blastopore lip)?  (1 pt) Explain (in one or two complete sentences.) (4 pts)










b)  Did this transplantation change the fate of the host embryo?  If so, how? (5 pts)









5.  Niewkoop (10 points)

A.  Niewkoop assayed the fates of explants from cleavage stage amphibians.  How did the cells differentiate when

  1.  animal caps were explanted? __________________________________
  2. vegetal cells were explanted?___________________________________
  3. How did animal cap cells differentiate when co-incubated with vegetal cells?



B.  What can you conclude from the experiments in which the animal caps were co-incubated with vegetal cells?  Explain.









6. Homeosis (10 points)

A. Define “homeotic mutation”:





B. Give an example of a homeotic mutation that affects Drosophila A-P fate specification.


a.      Name of the gene that is mutated: _________________________


b.      Mutant phenotype: ______________________________________



c.      Nature of the mutation (loss-of-function, ectopic expression, etc):


d.      Normal function of the wild type gene:





7.  p53 (8 points) 

Why are cancers involving defects in the p53 gene so difficult to treat?





8.  Bicoid (20 points) 

In the specification of the Drosophila anterior-posterior (A-P) axis, gradients of two morphogens, Bicoid and Caudal, are important.


A. Describe the mechanism by which the Bicoid protein gradient is established.







B. Describe the mechanism by which the Caudal protein gradient is established.






C. Describe the evidence that Bicoid is necessary for anterior fate specification.





D. Describe the evidence that Bicoid is sufficient for anterior fate specification.





E. You mate Bcd+/bcd- female flies to  Bcd+/bcd- male flies.  Progeny with the following genotypes are produced in a 1:2:1 ratio: Bcd+/Bcd+ : Bcd+/bcd- : bcd-/bcd-.  Remembering that the bicoid (bcd-) mutant is recessive, what are the phenotypes of each genotypic class? Explain your reasoning.