Embryology Biology 441 Spring 2010 Albert Harris
Review Questions for First Exam
Additions were made to questions 4 and 5 on Tuesday morning about 10:30 am. 1) What are the 3 primary germ layers? 2) List tissues and organs that develop from each of these three. 3) Name and describe the process by which the cells of embryos are subdivided into these 3 germ layers 4) Contrast this process in embryos of *sea urchins, *frogs & salamanders, *teleost fish, *birds & reptiles, and *mammals. You should be able to make sketches of sequential stages of development in each of these. *5) Is there any relation between especially large and yolky eggs and the geometry of gastrulation? (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. 6) Is mammal gastrulation more like gastrulation in echinoderm embryos, or frog embryos, or bird embryos? (*why?) 7) Neurulation subdivides what into what three subdivisions? 8) Name these 3 subdivisions; what parts of the body, and what cell types develop from each? 9) Ordinary motor nerves ("motor" in the sense of stimulating muscles to contract) develop from cells of the neural tube; but what special kind of motor nerves develop from a special subset of neural crest cells? 10) List at least 4 cell types that develop from neural crest cells. **11) Try to think of any logical reason why the skeleton of the face develops from neural crest, although in the rest of the body skeleton develops from mesoderm (usually somite mesoderm). Do you think it might have something to do with the bone-like dentine layer of teeth being derived from neural crest cells? 12) Placodes develop by thickening and infolding of certain spots on the somatic ectoderm; please name 3 examples. 13) Which placodes separate entirely from the surface? Which develop sensory and nerve cells; which become transparent? 14) Please make lists of pairs of tissues in which one tissue induces a change in differentiation of the other. 15) Make lists of induction in which both cell types induce a change in the other, as well as being induced by it. 16) What tissue induces neurulation and the subdivision of the ectoderm? 17) From the diagram shown in class, and the near completeness of the second embryo, does the notochord seem to be producing some inductive changes in mesodermal and endodermal cells, not just the induction of a second neural tube? *18) What sort of abnormality might you expect if a thin sheet of impermeable mica were surgically inserted just below the dorsal ectoderm, between it and the mesoderm? 19) Describe and name at least three specific examples of human birth defects that result from incomplete or failed fusions of sheets of cells. *20) Invent fictional birth defects that might possibly result from fusion between adjacent sheets of cells that don't normally fuse. *21) Invent fictional birth defects that would result from failure of fusion between sheets of cells that always do fuse in normal development. *22) Because ectoderm that normally comes in contact with notochord normally neurulates, but will NOT neurulate if it is dissected away or otherwise prevented from contacting the notochord, do you think that induction would have been recognized as important and given the Nobel prize based on the failure of neural tubes to form in endoderm that had been prevented from touching the notochord? 23) Grafted Hensen's nodes from chick embryos can induce second neural tubes and whole second embryos, not only in early bird embryos, but also in mammal embryos (which I guess become chimeric for their notochord): what do you think this means, in terms of mechanisms and similarity of signaling mechanisms in different kinds of animals? 24) What other experiments do these results suggest to you? 25) What other major similarity is there between the Hensen's node and the dorsal lip of the blastopore (hint, the cells of which mesodermal organ are internalized at both these locations. *26) There must have been a gradual evolutionary transition from embryos with blastopores to embryos with primitive streaks. Suggest what changes in the movements of future mesoderm and endoderm cells would have produced this transition. 28) Pairs of somites develop along both sides of what mesodermal organ? 29) Each somite subdivides into what three parts, one whose cells differentiate as skeletal muscle, another forms skeleton, and the third forms the inner-leathery layer of the skin. 30) Which of these three subdivisions then subdivides into an anterior and a posterior part. Each anterior part then fuses with the posterior part of what, so as to form what anatomical structure. **31) Somite cells all disperse, and later in development you can only see remnants of where they had been: Can you suggest functional or mechanical reasons why the vertebrate body is segmented by transient rather than permanent blocks if cells. In fact, why use aggregated blocks of cells at all? People hypothesize that wave-like gradients of diffusing chemicals are what control where the somites are formed; so why not have those chemical gradients directly determine which cells will differentiate into muscle, bone and dermis. (Why not eliminate the middleman?) 32) What are chimeric mice? Chimeric mouse-rats, sheep-goats. Why don't their immune systems attack each other; or, rather, what does it tell us about how the immune system avoids attacking cells of its own body. 33) If a second polar body of a cross-breed mouse embryo were to fuse with another mouse sperm, and then go on to form part of the tissues of the animal that resulted, would you consider this animal a chimera. 34) Does the viability of chimera tell us anything about differences and similarities between their cytokines, their inducing substances, etc. **35) Can you think of any scientifically useful purpose that would be important enough to justify making chimeras between human blastula stage and equivalent stages of early development of other species? 36) Figure out how chimeras that combine genetically different mice have been used to prove that skeletal muscle cells become syncytial (=multinuclear) by fusion of separate cells, rather than by repeated mitoses without cleavages. How can chimeras be used to prove the same question about osteoclasts, or any other multinuclear cell types. 37) Suppose that, by bad luck, cells of the different species would not fuse with each other: how would that give you incorrect answers to the experiments in the preceding questions? 38) How can those same chimeras be used to gain strong evidence that cancers are clonal, in the sense of starting in one cell, and then continuing in the mitotic daughter cells of that original cancer cell, and only in some special examples of viral-causes cells will cancer spread from cell to cell. *39) A very important question in immunology is whether self-tolerance results from embryonic destruction or inactivation of all lymphocytes whose binding sites would bind to any molecule found in the embryonic body, versus this destruction or inactivation needing to go on throughout adult life, based on inactivation of lymphocytes whose binding sites fit any molecules present in large enough concentrations.
Can chimeras help solve this question? Hint: if you formed a chimera from embryos of two species,
raised them to adulthood, and then somehow eliminated/killed off all the cells/nuclei of one of the species; then experiment to see if the remaining former-chimera organisms would accept grafts from the species whose cells/nuclei had been killed off. 40) What is polyspermy? Is it good or bad? Bad for the oocyte but good for the sperm? The reverse? Or bad for both? 41) Which differentiated cell type on the body have a resting potential, caused by about 15 times the concentration of potassium ions inside cells as compared with the concentration of potassium ions in the fluid surrounding the cell, combined with the plasma membrane being significantly more permeable to potassium than to other ions. 42) What explains the paradox of the resting potential being positive outside /negative inside, although it is caused by positively charged potassium ions being more concentrated inside. 43) Compare a nerve action potential to the fast block to polyspermy (differences as well as similarities). 44) Compare the secretion of synaptic vesicles to the slow block to polyspermy (differences as well as similarities.) 45) How could somebody invent new birth-control methods based on either activating or inhibiting either the fast or slow blocks to polyspermy. *46) Which is better, more practical or more moral: preventing conception by setting off the anti-polyspermy mechanism; or producing non-viable triploids, or tetraploids etc. by preventing the polyspermy mechanism from working. Answering this question would mean explaining your reasoning in a way that demonstrates that you understand the biological phenomena. Either alternative answer could be correct. *48) What about contraception by a drug that blocks completion of the second polar body. How could that work? 49) What major discovery was made by Hans Driesch, in about what year, and how did this discovery change his beliefs about causes of embryonic development? 50) Spemann received the Nobel prize for discovering what embryological phenomenon. 51) What are at least 4 examples of this phenomenon, in addition to the one that Spemann's graduate student discovered? (What was an example of this phenomenon tat was discovered by a professor in this department, before he came here?) *52) How can what Spemann discovered help explain what Driesch discovered, but couldn't make sense of? 53) What groups of animals have very regulative development? 54) What groups of animals have very mosaic development? 55) What are some examples of ooplasmic segregation being used to control the locations where particular cell types will differentiate? *56) Argue pro or con whether mosaic versus regulative development is just a quantitative difference in how early or late in development cells become irreversibly committed to differentiate into particular cell types, as opposed to mosaic development resulting from some qualitative difference in the mechanism of spatial control of cell differentiation. 57) If embryos of a certain group of animals use ooplasmic segregation to control where each cell type will differentiate, then would you expect their development to be regulative or mosaic? 58) Does induction ever control the differentiation of cells in embryos with highly mosaic development? (Give an example, if there are any) 59) How can you cause a vertebrate embryos to develop two hearts? 61) Why do bird and mammal embryos develop three pairs of kidneys?
62) In the development of the heart, do we first form a one-chambered embryonic heart, then replace it with a two chambered fetal heart, which we use to pump blood while we construct the 4-chambered heart that we will use after birth and for the rest of our life? 63) In what way is the imaginary sequence of hearts analogous to what actually happens in the embryonic development of kidneys? 64) The sperm ducts of male mammals, reptiles and birds was used for what purpose during embryonic development, when no sperm were being produced? 65) Does the future oviduct ever serve as a urine duct? (hint:no) 66) The lateral plate mesoderm splits into what two layers, with what between them? 67) The oral and nasal cavities become separated in some vertebrates, but not others: how is this separation accomplished, in which group of vertebrates does the separation occur, and is there a birth defect in which the separation is incomplete? 68) A serious birth defect that sometimes occurs is that a hole connects the right and left ventricles of the heart. To what other birth defects is this analogous? (Does it result from something having cut or cleaved a hole through the septum between the ventricles? Hint: no). 69) Until birth, blood flow and oxygenation of blood is not abnormal in babies with holes connecting their two ventricles: why not? Please explain why oxygenation of blood then suddenly become very abnormal in these babies, at the time of birth? 70) Do mammal embryos ever develop a hole connecting their right and left atria? (Trick question!) 71) What is fetal hemoglobin? When does a person have fetal hemoglobin in their blood, instead of adult hemoglobin? What happens if a person continues to make fetal hemoglobin, instead of adult hemoglobin, all their life? 72) If you invented a drug or other treatment that would cause people to continue to make fetal hemoglobin, instead of adult hemoglobin, then what genetic disease could you cure with this treatment that you had invented? 73) If some chemical pollutant had the effect of inhibiting fusion between epithelial cell sheets, then make a list of all the different birth defects it could produce. 74) In what sequence do somites become separated from each other? First on one side, then on the other? First near the front, then one pair after another toward the rear? First at the rear and gradually toward the anterior? First in the middle, and then sequentially toward both ends? Or what? 75) Contrast the rearrangements of cells that occur when somites are formed in mammal and bird embryos, as compared with frog embryos, and as compared with embryos of the non-vertebrate chordate Amphioxus. 76) If you had a drug or treatment that could cause more somites to form on one side of the body than on the other side, then list all the anatomical abnormalities this would be expected to produce. 77) Describe as many examples as you can in which differentiated cells have crawled from one part of the embryo to another. (for example: the cells that form the dentine of the teeth). 78) In embryos of mammals and birds, the diameter of the notochord is much smaller than the diameter of the neural tube; but in embryos of salamanders and frogs, the notochord is almost as big as the neural tube, and sometimes bigger. What sense does this make in relation to the function of the notochord in swimming? (Hint: As compared with its inductive function.) *79) The notochord is a long cylinder with rounded ends. It consists of vacuole-filled cells tightly wrapped by collagen fibers, aligned in spiral directions. Based on the web site photograph of the fluorescent collagen wrapped around an embryonic blood vessel, suggest a possible mechanism for the embryonic shaping of the notochord. Incidentally, the currently accepted theory on this subject is that notochord cells reach out sideways with cytoplasmic protrusions, and then contract these inward. Notochord cells tend to be highly flattened, perpendicular to the long axis of the notochord, so that the cells are shaped and arranged like a stack of coins. How can these shapes be produced by cellular forces? Nobody knows: nobody even knows how to find out; the question is whether you can build hypotheses using available information. 80) Hair, scales and feathers are made of epidermis (=somatic ectodermal cells) but their locations are somehow controlled by aggregations of dermal mesenchymal cells (from the dermatome). Would you consider this an example of induction, in the embryological sense? You can argue either pro or con, so long as you demonstrate knowledge of embryology. 81) Contrast the timing and geometric patterns of early cell divisions in embryos of mammals as compared with embryos of birds, amphibians, and teleost fish. 82) Sperm secrete the enzymes in their acrosomes as a result of fusing the membranes surrounding the acrosome with the plasma membrane (that surrounds the whole sperm). What are two other examples of plasma membranes fusing with another membrane, i.e. that occur during fertilization?
83) Compare and contrast the slow block to polyspermy in sea urchins as compared with mammals. Do they both have a slow block to polyspermy? Which is more complicated? 84) Where and how do the eggs of birds, reptiles and platypuses get their shells and egg white? Are these materials really part of the oocyte? 85) Do mammal oocytes have anything like an egg-shell? 86) Where should a developing mammal embryo be located by the time that it secrets enzymes that digest the zona pellucida ("shell") surrounding it? 87) What will probably happen if this escape from this shell occurs too soon, or if the mammal embryo has not traveled far enough down the oviduct? (hint: the result will cause much pain, require surgery, and may result in sterility.) 88) 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. 89) Functionally, explain these differences (in the preceding question). (hint: because sperm need to be ... whereas oocytes need... ) 90) If something goes wrong ("non-disjunction") and a chromosome is lost, or an extra chromosome is gained, during one of the meiotic divisions, then which (the oocyte or the sperm) is more likely to develop abnormally and be unable to participate in fertilization? And explain why. 91) The pigmented retina, the neural retina, and motor nerves all develop from which subdivision of which germ layer? 92) Kidneys and sperm ducts develop from which subdivision of which germ layer? 93) Skeletal muscles, skeleton and the inner layer of the skin develop from which subdivisions, of which part, of which germ layer? 94) List as many examples as you can in which a boundary between two (or more) organs or differentiated cell types corresponds to a fold in some embryonic epithelium. 95) What is the defining property of the animal pole of an oocyte? 96) In frog and salamander embryos, the animal pole also has what other special properties? 97) Embryos of what kind of animals form their blastopore at the vegetal pole? 98) 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.) 99) Where are "deep cells" formed, and what do they develop into? Where are they relative to the "enveloping layer"? 100) Imagine that a blastocyst developed two inner cell masses (instead of the normal one inner cell mass), or that an inner cell mass developed two primitive streaks (instead of just one), or that two blastocysts formed inside one zona pellucida: what would be the result of each of these abnormalities? (Hint: Could all three produce the same result? And introductory textbooks almost always explain this result by a fourth abnormality, which the zona pellucida makes impossible!) 101) List as many examples of ingression as you can think of (At what stages of embryonic development, in embryos of which kind of animal, in the creation of which populations of cells, that develop into what?) 102) Sketch a gastrulating amphibian embryo, viewed on the side where the blastopore is located, and with many small arrows showing the relative directions and speeds of cell movements. 103) What is the connection between the blastopore and the archenteron? 104) When is there a connection between the stomodeum and the archenteron? 105) Mesoblast cells are formed where? In embryos of which kinds of animals? 106) What is the relation between Hensen's node and the notochord? 107) Sketch a pluteus? What were plutei thought to be, by their first discoverers? What are they really? 108) List as many differentiated cell types as you can whose geometric location relative to the rest of the body is the same as the location of the part of the cytoplasm of the oocyte from which they developed, relative to the rest of the oocyte. (Hint: Trick question: Are there any such cell types?) 109) About what distance is the diameter of a mouse oocyte? A human oocyte? A sea urchin oocyte? A frog oocyte? A chicken oocyte? 110) Discuss whether true or false: Embryonic regulation can only occur if parts of the embryo can develop into what would normally have developed from the tissues adjacent to it. And, that, in turn, could only occur when each bit of developing tissue normally inhibits the surrounding tissue from differentiating into the same cell types or organs (as the tissues doing the inhibiting). Does your answer apply equally to examples of embryonic regulation in which two early embryos are fused with each other? Regarding mosaic development, would you make the reverse statement? (That tissues can't substitute for their neighbors, and [or because they] don't inhibit their neighbors from developing along the identical pathway as themselves.) I will be grateful for similar questions submitted by students in the course, and some of these will be used on the exam.
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