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On which specific kind of teleost is research now being concentrated? What are its advantages, relative to other vertebrates? What are its disadvantages as a model system to help understand the mechanisms of human development? What are two other species of teleosts that have been the subject of considerable embryological research? What are at least two examples of kinds of fish that are NOT teleosts? What extraembryonic membranes are part of teleost fish development? What other extraembryonic membranes are part of the embryonic development of reptiles, birds and mammals? What are "deep cells"? What do they become in development? What is the embryonic shield? Are there any good examples of epiboly in fish development? Why did earlier embryologists expect that some part of the enveloping layer, and probably part of its edge, would undergo invagination? What experimental evidence seemed to confirm this explanation? What mistake did the experimenter make in this case? * By means of what control experiments could he have detected the likelihood of this mistake? * Can you invent some other kinds of experiments by which experimenters could have proven whether or not the enveloping layer underwent invagination? What other experiments (hint: using actinomycin) seemed to show that transcription was completed at a very early stage of development in teleosts? What seems to have been the actual explanation for those results? * By what control experiments could one test for this possibility? Are there any examples in which embryonic cells reach the same end result by means of what seem to be very different mechanisms? (Hint: at least by passing through geometrically-different intermediate stages?) How do some people think this is related to the field of physical chemistry known as thermodynamics? What are the three main subdivisions of the ectoderm? Placodes form from which of these subdivisions? In what part of the body do placodes form? List the specific organs that develop from placodes? *What are neuromast cells? What biological sense does it make that we use the inner ear to detect gravity, sound, and also rotational movements? What are a similarity, and a difference, between lateral line organs and the semi-circular canals? Describe the embryonic development of the lens relative to the eye-ball? From which does the optic nerve form? The optic nerve connects what to what? What and where is the optic chiasm? Most of the somatic ectoderm develops into what part of the body? How is this part related to the dermis? From what subdivision of what germ layer does the dermis develop? What are dermal papillae? How are they related to scales feathers and hair? Do they actually become some part of feathers? *Would you regard this as a case of embryonic induction? *Why or why not? What is the stomodeum? What organs and tissues develop from the stomodeum? How is the stomodeum related to the archenteron? What is a synonym for ectomesenchyme? What are seven specific cell types or organs that develop from cells of the ectomesenchyme? * Imagine the symptoms of a genetic syndrome or birth defect in which all of these develop abnormally. What are four specific kinds of birth defects that result from failure of sheets of cells to fuse together normally? Why might you not expect teleost fish embryos ever to suffer from one of these birth defects? Why should women who might become pregnant be careful to take folic acid (vitamin B12)? How were Japanese quail used to find out (and prove conclusively) which parts of the body develop from neural crest, or from other embryonic rudiments? * For example, describe a hypothetical experiment by which Japanese quail embryos could have been used to find out for sure whether mouse odontoblasts can really induce bird stomedeal cells to form tooth enamel? What cell types and parts of the body develop from neural tube ectoderm? What are the names of the five main subdivisions of the brain in vertebrates? Can you name specific structures that develop from the anterior four of these? What are rhombomeres? Describe them. Contrast the embryological origin of motor nerves versus sensory nerves? What about the special kinds of sensory nerves of the eye, nose and ear? What is the genus name of chickens? What are the advantages and the disadvantages of doing embryological research on bird embryos? What is the cerebrum? What is the hippocampus? Where does the cerebellum develop? Which part of the brain is most important for balance and coordination of musclular movements? Describe the shape and location of Purkinje cells? Can you think of at least two places in the body where nerve fibers run past other nerve fibers at right angles (90 degrees)? * In terms of alternative theories about the guidance of nerve fiber formation, would you expect any of these mechanisms to be able to cause nerves to extend in directions perpendicular to each other? Briefly explain several alternative kinds of mechanism that have been proposed to explain guidance of nerve axon outgrowth. Is there any relation between axon formation and DNA synthesis by nerve cells? In the developing neural tube, where do the cells undergo mitosis and cytokinesis (= cell division = cleavage)? Is this because only the cells in that area are growing and going through the cell cycle? (hint: no) What is a nerve growth cone? Is extension of nerve fibers simply a matter of growth, in the sense of enlargement (hint: no again!) How is nerve fiber formation related to amoeboid cell locomotion? The optic nerve is made out of axons that are extended from nerve cells that are located where? (In other words, where are the nuclei of these nerve cells? And from what part of the embryo do they form?) In birds and ampibians, what specific part of the brain does the optic nerve connect to? What is the geometric pattern of this connection? Hint: what is meant by a neural projection? Mutations of the mouse genes named waltzer, reeler, weaver, etc. cause what specific part of the body to develop abnormally? What are the most apparent phenotypes of these mutations? What sorts of proteins might these genes code for?(Invent some possibilities! Think about hypothetical mechanisms for guidance of growth cone locomotion.) What is a ganglion? In what sense are "ganglion cells" not really part of a ganglion? In the retina of the eye, which cells actually detect the light? Which cells actually connect to the brain? Describe the path followed by the optic nerve growth cones? In animals that have stereo vision, what is unusual about the paths of some of these growth cones? What is the optic chiasm? In terms of the various theories about the mechanism of guidance of nerve growth cones, is it easy or difficult to explain the optic chiasm? Explain why or why not? What are the epiblast and the hypoblast, and how are they related to each other? Are they found in the area opaca, or somewhere else? How is Hensen's node related to the primitive streak? How is Hensen's node equivalent to the dorsal lip of the blastopore? * What would it prove about evolutionary changes (or lack of changes) if it were possible to induce twinning in a chicken embryo by grafting a Hensen's node from a mammal embryo? * If embryos have an amnion, do they also have a Hensen's node? (hint: yes. But what's the connection; if any?) Are there any kinds of mammals that lay eggs? Are the oocytes of marsupials different from those of most mammals? What is the zona pellucida? Is it related in any way to the area pellucida? If you want to make chimeras between different species of mammals, what do you have to do to the zona pellucidas of their embryos? How are ectopic pregnancies related to whether a human embryo is located at the time of compaction and the breakdown of the zona pellucida? What is meant by implantation in mammal embryology? *How would you expect cells of the trophoblast to participate in the process of implantation? *Why would you not expect that cells of the inner cell mass would play any direct role in implantation? The "stem cells" now in the news are derived from what part of early mammal embryos? What kind of stem cells are found in bone marrow? (and umbilical cords!) Are any stem cells found in the brain? Are any of the stem cells in the adult body what the current political debate is about? At what stage of embryonic development do mammal embryos implant in the uterus? At this stage of development, mammal embryos are made of what two classes of cells? What is meant by "putting embryonic cells into tissue culture"? What is meant by saying that certain cells are totipotent? What now-common medical procedure generates large numbers of blatocyst stage human embryos (the mammal equivalent of the blastula stage)? Why does it generate this particular stage, rather than embryos at either earlier or later stages? What is usually done with these extra human blastocyts? What would many researchers like to do with some of these blastocyts? Why can researchers do such experiments in England, but rarely in the United States? Which stem cell cultures are US researchers allowed to use? What does the ASCB claim is wrong with these stem cell lines? Can you suggest some reasonably plausible ways to treat particular diseases, using stem cell cultures whose differentiation could be controlled at will, for example by adding certain protein growth factors to their tissue culture medium? * How, for example, might you use them to cure coronary arterial blockages? How is the trophoblast related to the chorion? How is it related to the amnion? Which of the extraembryonic membranes are directly in contact with the mothers tissue? *Why does the allantois have to store urine is many species of mammals, but not others? *How is the amount of this urine storage correlated with the degree to which the mother animal is incapacitated at the time of birth? In what three different ways can identical twins be formed in mammals? Which of the extraembryonic membranes are shared between the twins in each of these three cases (if any are shared)? What is meant by conjoined twins? Would you expect it to be possible for identical twins to develop from bird eggs? How does the formation of identical twins in mammals differ from the separation of the first two cells in frog embryos or sea urchin embryos? Describe the physical structure of the notochord? Describe the location of the notochord, relative to the neural tube, and relative to the somites. What is the mechanical function of the notochord in early fish and tadpoles? What adult human structures do many people (wrongly?) assume that the notochord develops into? What is the fate of most of the paraxial mesoderm? In what part of the body do somites NOT form? What is the prechordal plate? What are somitomeres? What do somites develop into? Describe the formation of somites? Is there any relation between the number of pairs of somites in an embryo and the structure of (which?) parts of the body that develop? Muscles of the arms and legs develop from what part of the embryo? Somites divide into what three or four parts?
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