Sample Exam Questions   Questions marked with a * are not easy, but you will gain a lot from thinking carefully about them. I won't ask many such difficult questions. A) List and briefly describe (which should include drawing a sketch of each) at least four morphogenetic cell movements. B) Describe and sketch several specific embryological example of invagination. The following are nine examples: Infolding of the archenteron in echinoderm embryos; or in amphibian embryos; or the infolding of the stomodeum of echinoderm, or amphibian, or mammal, or bird, stomodeums; infolding of the neural tube in embryos of amphibians, birds or mammals. C) Describe and sketch several specific embryological example of epithelial fusion. Fusion of the archenteron with the stomodeum, in embryos of echinoderms and amphibians. You may be able to think of more examples, and will learn more later. D) Describe and sketch several specific embryological example of ingression. In echinoderm embryos, formation of the primary mesenchyme (which secrete the skeleton) and the secondary mesenchyme (which differentiate into muscle cells) E) ...Specific embryological example of cell locomotion?...cell traction? F) Which of these morphogenetic movements consists of epithelial cells become converted into mesenchymal cells? *G) The neural tube of teleosts forms by rearrangement of a solid rod of cells into a hollow epithelial tube. This process is called "cavitation". In what sense is it the reverse of ingression? (You can also argue that it isn't the reverse, as long as you give reasons for your conclusion.) H) What is at least one other example in which a solid mass of cells rearranges to form an enclosed cavity? Blastocoel formation. I) What is a fundamental difference between the blastocyst of mammal embryos and the blastula of echinoderm (sea urchin) embryos? J) How similar are they? Make a sketch of each. How could you tell them apart? K) About what percentage of the cells in a mammal blastocyst will become parts of the body of the animal? L) What structures are formed by the other 95% of the blastocyst cells? M) List at least five examples of embryological changes in shapes or positions of organs in which the driving force was long believed to be growth, in the sense of enlargement and/or mitotic division of cells. Diagrams of six examples are shown in the drawing on which "Blastocoel enlargement" is written at the upper right side. Other examples are elongation of capillaries and nerve axons. *N) Suggest experiments by which you could test whether a an embryological process is directly caused by cell enlargement, or is caused by mitosis, or is caused by the exertion of traction by cells. *O) Sketch from memory the diagram of the branching railway tracks leading to 'brain", "sensory nerves", "skin", "notochord", "dermatome", "myotome", "sclerotome", "kidneys", & "heart". P) An exam question might consist of this branching pattern, with blanks instead of words, and you would be asked to fill in the blanks Q) Argue true or false: "The concept of embryonic induction is that the metaphorical railway switches in this diagram are controlled by specific signaling chemicals secreted by nearby cells." *R) Suggest possible reasons why geometric rearrangements of embryonic cells need to occur in order for the eventual 250 differentiated cells to be located in the correct anatomical locations, relative to each other. (I am guessing there must be some reason. Why not just form the nervous system by differentiation of cells that were already located in the interior of the blastula, etc.?) ?Perhaps because movements are an effective way of sharpening the boundaries between organs? ?Perhaps because physical forces are used as signals that contribute to induction of cell differentiation? ?Perhaps migrations of cells cause them to become located next to a sequence of different cells, from which they get a series of different chemical signals, that (for some reason) they need to receive one at a time, in certain sequences? ?Please suggest some other possible reason. *S) The last photograph of the January 9th course web page (The one with a wiggly orange line running horizontally across the middle) is a cross section through a posterior part of the brain. These wiggles are called "neuromeres", and were long believed to have no functional importance. Instead, they were assumed to be passive results of "growth pressure". Researchers then discovered two surprising facts: That functionally different nerves differentiate from each different neuromere. That different hox genes are transcribed in different wrinkles. What hypotheses can you propose to make sense of these correlations between nerve functions, transcription factor expression and geometric folding of this part of the floor of the hindbrain? T) Based on what you now know about some the normal cell rearrangements that occur during embryonic development, please invent some possible birth defects. For example, what if the edges of neural tube failed to fuse with each other? U) Chemical signals that can stimulate embryonic induction can also cause birth defects: Explain why you could have predicted this. V) Many scientists now hope to develop methods to re-grow damaged organs, starting with undifferentiated "stem cells". Explain why they will need to use chemicals that can cause embryonic induction. W) Explain the difference between holoblastic cleavage versus meroblastic cleavage. X) Compare amounts and distributions of yolk in oocytes of sea urchins, mammals, teleosts, amphibians, and birds. Y) Imagine that you discovered oocytes of some unknown kind of animal, could you predict whether they would undergo holoblastic or meroblastic cleavage, based on size of the oocyte, amount of yolk, and/or un-eveness of yolk distribution? Please explain. Z) Why does mammal gastrulation (i.e. gastrulation of mammal embryos) resemble bird gastrulation much more than mammal gastrulation resembles gastrulation of amphibian embryos?

 

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