Developmental Biology Name ___________________________

Midterm 1

1.  (10 points)
Sperm binding initiates a sequence of events in the egg that prevent fertilization by additional sperm.  Describe the slow block to polyspermy, including the roles of specific intracellular messengers.  Explain how this sequence of events inhibits polyspermy.

2.  (10 points)
Bindin mediates species-specific gamete recognition.  A colleague sent you purified bindin from two species of sea urchin, S. purpuratus and S. franciscanus, but the labels came off the tubes during shipping.  Thankfully, you have an abundant supply of gametes from both species.  Design an experiment that will allow you to determine which species each sample of bindin is from.  (Hint:  What does bindin bind?)
Describe the experiment and your rationale for the experiment.

Describe two alternative results of that experiment.  How would you interpret each result?
Result 1:

Result 2:

3. (10 points)

A. What are the major tenets in the theory of genomic equivalence?

B. What experimental evidence gives the strongest support for the theory of genomic equivalence? Explain.

4. (16 points) In amphibian eye formation, the head neural ectoderm contributes the optic cup while the lens develops from the head ectoderm. We discussed several experiments relating to this process, summarized as follows:

1. If an optic cup is surgically removed, the head ectoderm no longer forms a lens.
2. If an optic cup is surgically transplanted beneath head ectoderm, the head ectoderm forms a lens.
3. If an optic cup is surgically transplanted beneath trunk ectoderm, no lens forms.
4. If trunk neural ectoderm is transplanted beneath head ectoderm, no lens forms.

Answer the following questions about these experimental results, making sure to use the words “induction” and “competence” appropriately.

A. What do experiments 1 and 2 demonstrate?

B. What can be concluded from experiments 2 and 3? What cellular or molecular difference between head and trunk ectoderm might account for the different results?

C. What can be concluded from experiments 2 and 4? What cellular or molecular difference between optic cup and trunk neural ectoderm might account for the different results?

5. (12 points) The retinoblastoma protein (Rb) is a key regulator of the cell cycle.

A. At what point in the cell cycle does Rb function?

B. Describe the molecular function of Rb and how this leads to cell cycle regulation.

C. How is Rb activity regulated?

6. (16 points)

A. What cellular-developmental process is performed by caspases?

B. What are the two major pathways that regulate the activity of initiator caspases?

C. How do initiator caspases regulate the activity of effector caspases?

D. What are the three general classes of substrates for effector caspases?

7. (6 points)

A. Where in the cell are receptors for peptide signals (ligands) located?

B. Where in the cell are steroid receptors located?

8. (14 points) A. Define or describe autonomous specification. If a blastomere is removed from an early embryo and allowed to develop in isolation, what are the outcomes of the isolated blastomere and the remainder of the embryo compared their normal fates in an intact embryo?

B. Define or describe conditional specificaton (regulative development). If a blastomere is removed from an early embryo and allowed to develop in isolation, what are the outcomes of the isolated blastomere and the remainder of the embryo compared their normal fates in an intact embryo?

9. (6 points) In Drosophila, there is a key developmental regulator called Nanos. Using immunological techniques, Nanos protein is not detected in oocytes, but following fertilization the protein can be detected. What are possible levels at which this difference in Nanos expression could be regulated?