Embryology Biology 441 Spring 2011 Albert Harris
Review questions for first embryology exam:A star* means a difficult question; I won't ask very many such difficult questions.
You ought to be able to explain and label the parts of every photograph, drawing and diagram on any of the web pages posted for this course, up to this date.
What are polar bodies? What is the difference in "Ploidy" and DNA content between the first and second polar bodies? What is the definition of the animal pole of an oocyte or an early embryo? What other properties or peculiarities are found at the animal pole of most species? The name of the location at the extreme opposite side of an oocyte or early embryo is called by what name? What is a blastocoel? Where is it formed? Do embryos of all species form a blastocoel? Does it become any particular structure in your anatomy? Hint: no Suppose a sea urchin embryo failed to form a blastocoel, would that hinder ingression or invagination of future mesoderm and endoderm cells? Hint: yes: but why? The entrance to the archenteron is through what opening? The blastopore? The stomodeum? Gastrulation of what kind of animals occurs by involution? Could you draw a picture of an embryo undergoing involution, based on the videos you were shown in class? What is cavitation? Give an example? Suppose that a sperm fused with a second polar body; might it then develop into some part of the person who develops from that oocyte? (explain your reasoning, pro or con.) By what evidence might you be able to detect that part of a person's body developed that way? (hint: you wouldn't actually need to see it happen.) If the spindle of a meiotic division (of an oocyte) got moved away from the animal pole, then the cleavages would divide to oocyte into more equal parts (i.e. either one or both polar bodies would be much bigger, even as big as a quarter or half the oocyte). What if such abnormal polar bodies developed as parts of the body? What is meant by invagination of an epithelial cell sheet? What is a specific example? What is meant by ingression of cells from an epithelial cell sheet? What is a specific example? What are some examples of fusion between epithelial cell sheets during embryonic development? In fact, several human birth defects ("spina bifida" is an example) are caused by FAILURE of certain epithelial cell sheets to fuse with each other? Suggest possible improvements in medical treatment of such defects, that would become possible if you discovered a particular enzyme or signal molecule that would stimulate epithelial cell fusion? Conversely, imagine a drug that stimulates epithelial fusion (as a side effect), and suggest as many birth defects as you can imagine that this drug might tend to cause, if a woman took that drug during pregnancy. Who was Driesch, and approximately when did he discover what? What did he conclude from this famous discovery? What do you conclude? Did Driesch use embryos of a species with mosaic development, or not? What if he had used C. elegans (nematode) embryos? How would that have changed his observations? How would that have changed his conclusions? Hint: Maybe C. elegans don't have entelechies? Would the results of the Roux "hot needle" experiment have led you to predict a different result in Driesch's blastomere separation experiments? (Hint: yes; but explain why.) Is there a correlation between cell volume and ploidy in animals? (hint, yes; on one of the web pages, there is a diagram of what an embryologist named Fankhauser observed on this subject. * Fankhauser's observations presumably result from something about how the cell cycle is controlled relative to cell volume. Suggest how the "start" checkpoint would need to be affected by DNA quantity (or maybe chromosome number?) and cell volume, in order to produce (explain) the patterns of cell sizes that Fankhauser discovered. Researchers who study zebra fish sometimes need to produce fish that are entirely homozygous for every one of their thousands of genes. To do this they expose sperm to enough ultraviolet light to destroy all their DNA, then fertilize oocytes with these sperm, and then use brief heat shocks to inhibit the first mitosis. Can you explain why these embryos develop into diploid fish that are homozygous for all genes? What if they didn't inhibit this mitosis? (The resulting fish would be...?) What if researchers instead used heat shocks or hydrostatic pressure to block the second meiotic division? The fish produced would have both sets of chromosome from the same... what? In principle (if the results were viable) how could you use variations on these methods to make fish that are haploid, tetraploid, octaploid, or have five sets of chromosomes? Would the resulting fish have smaller or bigger cells (than normal diploid fish)? Would the resulting fish have more or fewer cells? By what method do researchers cause development of chimeric mice? Mouse-rat chimeras? Do you think it would be practical to make chimeras between two species of fish? Approximately how would you go about this? At synapses, vesicles of neurotransmitters are secreted from vesicles, in a process that is analogous to the combination of mechanisms by which polyspermy is prevented. List as many similarities as you can think of. The fast block to polyspermy is analogous to nerve impulse in what ways? There are several.
New forms of contraception could be developed from inhibitors of which events in normal fertilization. What about drugs that stimulate certain events that normal during fertilization? Suppose that the plasma membrane of some differentiated cell type was very permeable to sodium ions, but not very permeable to potassium ions, but its sodium pump moved ions across this membrane in the normal directions, would such cells have a resting potential? Would this voltage be positive inside relative to negative outside, or the reverse, and why? Could such cells propagate the equivalent of action potentials? Would that require voltage gated potassium channels? Or what? The effect of putting an unfertilized oocyte in water with a high concentration of potassium would be what? The cytoplasmic concentration of calcium ions changes in what way during feritilization? Argue pro or con: Although the two extra embryonic membranes of teleost fish evolved completely independently from the four extra embryonic membranes of reptiles birds and mammals, the yolk syncytial layer is most closely analogous to the yolk sac, and the chorion in most closely analogous to which layer in fish? It so happens that many species of live-bearing teleosts have evolved: make an educated guess as to what sort of (placenta-like) connection they develop connecting the mother's tissues to the early embryo. Actually, what has really evolved is quite strange, and not what any sane person would be likely to guess. What are the three components that the somites break up into? Why is it difficult to study somitogenesis? Where are mesenchymal condensations found? What is the one mechanism shown to make confluent mesenchymal cells form condensations? About what distance is the diameter of a mouse oocyte? A human oocyte? A sea urchin oocyte? A frog oocyte? A chicken oocyte? Contrast the time of the meiotic divisions in spermatogenesis versus in oogenesis: time relative to differentiation of these cells, and also time relative to fertilization. Functionally, explain these differences (in the preceding question). (hint: because sperm need to be ... whereas oocytes need... ) What is the defining property of the animal pole of an oocyte? In frog and salamander embryos, the animal pole also has what other special properties? Embryos of what kind of animals form their blastopore at the vegetal pole?
What are the three primary germ layers? Contrast the timing and geometric patterns of early cell divisions in embryos of mammals as compared with embryos of birds, amphibians, and teleost fish. Be able to draw diagrams of major stages of embryonic development of sea urchins, frogs and salamanders, birds, mammals, and teleost fish. What is the connection between the blastopore and the archenteron? When is there a connection between the stomodeum and the archenteron? Scientists use the word "chemotaxis" to refer to several fundamentally different combinations of cell behavior (responses to differences or changes in chemical concentrations). Explain as many of these different combinations of behaviors as you can. *Maybe you can even think of some new ones. What does haptotaxis mean? Invent several different ways in which cells could respond to substratum adhesiveness that would probably be regarded as haptotaxis even though they are different (analogous to the different forms of chemotaxis). Describe three methods that have been used to quantitate contact inhibition. *If possible, invent a fourth. Invent criteria by which you could quantitate chemotaxis. If I show a video of cells undergoing chemotaxis (i.e. show the video during the exam) you should be able to decide accurately which of the versions of chemotaxis is being used. List advantages of zebra fish as an experimental organism, especially for discovering how genes control development. Describe the life cycle of Dictyostelium. What function does chemotaxis serve in the life cycle of Dictyostelium? In what sense is Dictyostelium even more regulative than sea urchin eggs? What happens if you cut a Dictyostelium "slug" into pieces? How many pieces can you cut them into, and get the same result? Compare invagination, involution, and ingression in gastrulation of birds, sea urchins, and reptiles (if appropriate). Is there any relation between especially large and yolky eggs and the geometry of gastrulation? (hint: yes) Can you describe the sorts of differences that occur, in embryos with very large amounts of yolk, as compared with those having less yolk. Is mammal gastrulation more like gastrulation in echinoderm embryos, or frog embryos, or bird embryos? (*why?) Neurulation subdivides what into what three subdivisions? What are the differences between a blastocyst stage of development and the blastula stage of development? (Differences include what kinds of animals go through these stages, what parts of the body will develop from each, and where gastrulation will occur.) Where are "deep cells" formed, and what do they develop into? Where are they relative to the "enveloping layer"? Sketch a pluteus. What were plutei thought to be, by their first discoverers? What are they really? What groups of animals have very regulative development? What groups of animals have very mosaic development? What are the four extraembryonic membranes in bird embryos? ...in reptile embryos ...in the placenta of human and other mammals' embryos? Which combinations of germ layers are each of the mammal germ layers made of? Explain the ways in which identical twins can occur. What happens when conjoined twins are formed? What tissues and organs develop from mesoderm? Compare the function and fate of the notochord in fish, amphibians, birds and mammals. What parts of the body develop from endoderm?
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