Review Questions for Second Examination.Embryology Biology 441 Spring 2008 Albert HarrisNOTE: some new questions have been added since this was first posted. Please start from the beginning to make sure you haven't missed anything.TQ means "thought question": Something you were not specifically told but ought to be able to figure out, based on knowledge you learned. The exam will contain thought questions.What are three examples of membrane fusion that are normal parts of fertilization? For each one of them, which other events in fertilization would fail if that fusion did not occur? What are acrosomes? Where are they located? What kind of cells have acrosomes? What do acrosomes contain? When are they formed? Are they considered special kinds of lysosomes? (Hint: They can be. But in what sense?) What are cortical vesicles? In what part of what cells are they found, up until what event? About how many cortical vesicles (hint: 10,000 to 20,000) does an average oocyte have? When do they disappear? With what purpose do they disappear. By what means, and triggered by what? TQ: If a (recessive!) mutation somehow prevented formation of cortical vesicles, then what would be the phenotype of that mutation? Make a reasonable guess what name might be given to the (normal) gene whose mutation prevented cortical vesicle formation. Similarly, make equivalent deductions for mutations that prevent formation of the acrosome. TQ: Can you invent genetic screens that would be useful for discovering what genes code for proteins that are needed for the formation and proper function of cortical vesicles and acrosomes? Where, relative to the body, does fertilization occur in the following kinds of animals: Sea urchins, mammals, birds, frogs, salamanders, some kinds of fish? (Hint: Does fertilization occur inside the mother's body? At the upper end of the oviduct? At the lower end of the oviduct? Near the body, but outside? Some random location outside the body?) What about some other kinds of fish? For species that release their unfertilized eggs onto the water, what are some mechanisms that are used to guide their sperm to eggs of the correct species? What is chemotaxis? (remember Dictyostelium, but now think about sperm that need to find their way to ripe oocytes; ripe in the sense of being ready to be fertilized). If sperm accumulate near eggs, is chemotaxis the only possible cause? Hint: Does flypaper have to smell like garbage? Might it work better if it did? What are at least four important differences between meiosis and mitosis? What are some similarities? When does meiosis begin and when is it finished in the development of sperm? When does it begin and when is it finished in the development of oocytes (in humans, for example)? What are the gonads called in the two sexes? Where are gonads located in the two sexes? In what one group of vertebrates is this location of gonads different in one sex than in the other sex? Is this difference in location because they develop from different embryonic germ layer subdivisions, or what? Hint: No? What has been the main theory about this difference in location? TQ: Why do you think male birds have an air duct running close to their testes, and connected to their lungs? TQ: Can you invent experiments that might be able to prove or disprove this theory about the reason what mammal testes are such a vulnerable and air-conditioned location? What is meant by the "blocks to polyspermy"? What is polyspermy? If polyspermy occurs, what will be the fate of the oocyte and (all?) the sperm that have fertilized it? If a mutation occurred that caused polyspermy to be more frequent, then would natural selection cause this mutation to increase or to decrease in the general population of that species? TQ: Perhaps would its frequency increase in males but decrease in females? What about a gene that not only allowed sperm to penetrate the blocks to polyspermy, AND ALSO gave their nuclei the power to destroy, inactivate or expel all chromosomes brought into the oocyte by other sperm? Is there a voltage difference between the inside and the outside of the plasma membrane of oocytes? Do any other cell types in the body also have such a voltage difference across their plasma membranes? What is the function of this voltage in oocytes? In terms of ions, ion concentrations, and permeability of plasma membranes to ions, what is the cause of this voltage difference? How can positive ions create a more negative charge on the side of a plasma membrane where their these positive ions have a higher concentration than on the other side? What is the sodium pump (membrane enzyme), and does it only pump sodium ions? If you caused an oocyte to become depolarized (lose this membrane voltage) before fertilization, then what would be the effect on fertilization? What would be the effect on fertilization if you used microelectrodes to keep this voltage difference the same after fertilization as it had been before? How might infertility be one of the symptoms of a mutation (or an environmental poison) that weakened the sodium pump? What is the fast block to fertilization? How is it similar to nerve impulses? The method of execution in North Carolina has been to inject large concentrations of potassium salts into the body: what effect would this have on unfertilized oocytes? What effect does it have on nerves and muscles (ALL of them, and not just those in the heart?) TQ: Would that hurt? Could anything hurt more? What are at least two different kinds of fast block to polyspermy? Which kind do humans use? Which kinds do sea urchins use? What are four major processes in the differentiation of a sperm? Do these events occur before or after their meiosis? What are the advantages of this timing of meiosis in males, and the advantages of the very different timing of meiosis in the differentiation and fertilization of oocytes? What are polar bodies? Where are they formed? By which kind of cells, and during what process? Why don't polar bodies form in the testes? TQ: What part of the body do polar bodies develop into? How many sets of chromosomes are there in a normal first polar body in humans? How many sets of chromosomes are in the second polar body? What if a second polar body accidentally contained fewer that 23 chromosomes? TQ: Could a first polar body possibly develop into part of the body? Would that make you a genetic chimera? Or a clone? TQ: Imagine some possible symptoms by which it could be deduced that a certain part of your body developed from an unfertilized first polar body. If a second polar body fused with a sperm, could it possibly become part of the body? TQ: Why would a second polar body be less likely to get fertilized than a first polar body would? (but why would the second polar body be more in need of fertilization by a sperm, in order to have any chance of becoming any part of the body? NOTE: Both polar bodies normally degenerate - except in parthenogenic species, however! Their oocytes (generally) resorb which (first or second) polar body? For what purpose do they take the contents of that polar body back into their cytoplasm? What would the result be if they resorbed the wrong polar body? Compare the meanings of "triploid" and "trisomic". Human and other species' chromosomes are assigned numbers according to what property? For example, why would a given chromosome be assigned the name chromosome number one; what about #8, what about #21. What is the meaning of, and the result of trisomy-8? What about trisomy-21? Trisomy-22? Who is that condition named after, and what did he do to deserve the honor? How does trisomy occur? i.e. what causes it? What are the results? What is the true diploid chromosome number of humans? But what was this number said to be for more than 50 years? In what ways did cowardice and hypocrisy cause this error? Not that any of us have anything against cowards and hypocrites, mind you! How many flagella do salamander sperm have? What about mammal sperm? How many do nematode sperm have? TQ: Can you invent some new kinds of contraception, based on what you have learned about normal events during fertilization? Inhibitors of acrosome enzymes? Inhibitors of cortical vesicle enzymes? Inhibitors of membrane fusions? Inhibitors of membrane voltages? Inhibitors of electrical depolarization of cells? (The latter is how local anaesthetics work, by the way!) What phenomenon did Hilde Proesholdt discover, working for her PhD in whose laboratory, where and approximately when? TQ: What would you guess she was trying to discover, instead of what she did discover? What did her discovery imply about normal mechanisms of embryonic development, such as why the neural tube and brain develop exactly from the part of the ectoderm closest to the notochord and somite mesoderm; and why the lens develops right next to the rest of the eye? TQ: Does it surprise you that embryonic induction has also been proven to occur in nematodes? Why, or why not? Does it please you to know that a certain UNC Biology Department Professor (not me! Nothing to do with me! His name supplied on request.) earned his job here by discovering induction in C. elegans? TQ: Why did people tend to expect that induction would to occur more (or only!) in species with regulative development? Does induction help explain regulation? Why couldn't scientists discover the chemical causes of primary induction? (And please don't just tell me "Lack of modern molecular methods" It's more fundamental than that.) SuperTQ! Figure this one out, and I will buy you lunch: What is the common feature of the reasons for failure to discover the inducing substance and the long delay in discovering the cell-cell adhesion proteins, like the cadherins? What phenomena were discovered by Johannes Holtfreter? In what laboratory did he earn his PhD? Why did he later flee to Canada, and then to the USA? What was it about the USA that attracted him here, and caused him to stay? (Considering that it couldn't have been the weather, since he became a Professor at the University of Rochester.) What are a few specific examples of teleosts? Why is their cleavage meroblastic? What is meant by the words meroblastic and holoblastic? Eggs of which kinds of animals have holoblastic cleavage? Compare the shape of a teleost egg at the one-celled stage with the shape of an adult human eyeball. In order to produce this geometrical shape, what differences in the mechanical tension need to exist at different locations? (Assuming that there is a constant outward pressure on all parts of the eggs surface or the eyeball surface.) Briefly explain why human eggs, and those of nearly all other mammals, gastrulate in the pattern of birds and reptiles, even though we have holoblastic cleavage and they have meroblastic cleavage. What is epiboly, in the most general sense? Describe the gastrulation of teleost embryos. Is it possible for conjoined twins to develop from fish eggs? What about from bird and reptile eggs? What is the definition of the animal pole? Is its location correlated with a lower density of yolk, and a higher concentration of cytoplasm relative to yolk? Hint: Yes? So if eggs are free to rotate, then which end will turn upward? How could you use gravity (or centrifugation) to force abnormal re-distributions of yolk inside an oocyte, or an embryo at the 1, 2 or 4-cell stages. Explain how gravity has been used to cause amphibian embryos to develop two blastopores, and then to become two headed tadpoles. TQ: Compare that experimental result with the phenomenon credited to Spemann and Mangold. [What is analogous in the results? How are the causes analogous?] If you had a microneedle full of the bicoid protein, how could you reasonably expect to produce much this same result in what kind of embryos? 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? What decides the Anterior-Posterior axis of fly embryos (both in the sense of the original direrctional difference, and also in the sense of processes that go on during embryonic develoment)? Imagine if the molecular control of human development were very similar to that of flies: Then if mRNA coded for by a certain gene was found at highest concentrations in the feet of embryos, then what sort of birth defect would you expect to be produced by mutations in this particular gene? The genes that control development in flies are subdivided by scientists into how many families? Describe the phenotypes produced by mutations in each of these families. Do the genes of some of these families ever influence the transcription of genes of any of the other families? Are any of them influenced BY proteins coded for by genes of any of the other families? Do any of these genes code for transcription factor (proteins). Are mRNAs of any of these genes already present in the unfertilized oocytes? Which ones? TQ, why do the phenotypes of these genes (but NOT the others) depend on whether the mother fly was homozygous or heterozygous for the mutation, independent of which variant of the gene may have gotten discarded in the polar bodies? What is peculiar about the early cleavage divisions of fly and (most!) other arthropod embryos, up until about the 6,000 cell stage (in contrast to any vertebrate embryos)? What part of teleost fish embryos are somewhat like this; but how are they different? What are imaginal disks? How are they involved in the metamorphosis of maggots into flies, and caterpillars into butterflies? If the effect of a mutation is to cause a fly to develop an extra pair of legs where its antennae should be, what kind of mutation is this called? What went wrong? Do any other kinds of animals have genes with base sequences similar to the genes that can produce this kind of abnormality when mutated? If mutation of a gene sometimes caused embryos to develop with a tail at both ends, and no head, then what result would you expect if you did "in situ" staining for nucleic acids that have then same base sequences as these genes? TQ: Why might "Sleepy Hollow" or "Headless Horseman" get used as names for such genes? What is the function of the "Tin-man gene", in terms of phenotypes of mutations of that gene? Guess what effect the Cerberus gene can have? There really is a gene named that! What about a gene named Cyclops? What tissue induces which other tissue to differentiate into the neural retina? What about induction of the lens of the eye? What about differentiation of the lungs, liver and pancreas? What did C. H. Waddington discover about induction in bird embryos? What combination of experiments and observations does Scott Gilbert refer to as "Find it; Lose it: Move it!" ? TQ: Which parts of this experimental approach will fail or give misleading results in particular cases, 1) If two different chemicals both contribute to induction of the formation of a given organ? (and either one can produce by itself, without the help of the other, but usually does get that help) or 2) If a combination of two chemicals were needed to induce a given organ, neither of which can produce the effect by itself? Draw (sketch) the stages of cleavage and gastrulation and neurulation (if it occurs in that kind of animal, which neurulation doesn't in invertebrates) in embryos of each of the following: mammals, birds, frogs & salamanders, teleost fish, sea urchins. What is odd about neurulation in embryos of teleost fish, as compared with neurulation of most other vertebrates? What is meant by "ingression", "invagination", "cavitation", and "fusion of epithelial cell sheets". Please know at least two examples of each of these 4 kinds of cell rearrangements, including where, at what stage, for the purpose of forming what, and in embryos of what kind of animal, each category of cell rearrangement occurs. How can you tell from 30 feet away whether a clutch of frog eggs in your bird bath or swimming pool has been fertilized, or not? How big are oocytes? How many flagella do sperm have? TQ: In relation to the embryonic formation of anatomical structures, what is meant by "Tensegrity", the "Thermodynamic Theory" of cell sorting, and by "Anatomical Homeostasis" (now more often called "Shape Homeostasis")? Hint: Any or all of these concepts are related to those odd diagrams at the end of the Feb 18 lecture notes, that are labeled "Two kinds of causality".
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