Biology 104. Albert Harris Review Questions For The Third Examination April 11, 2005 What are genetic screens? Who earned the Nobel Prize for the results of their genetic screens for mutations that drastically alter structural development of fly embryos? Regarding genes of (Drosophila) flies that have been discovered to control embryonic pattern formation: What generalizations can you make? Most of these genes code for proteins that serve what function? (hint: they bind to specific ____ ________ on ___ and stimulate, or sometimes inhibit, what molecular process?) What different "families" of genes control embryonic development of flies? In what sense is one family # 1, and another #2, etc. Hint: What controls the transcription, and the subsequent locations, of the messenger RNAs of the genes in the first of these families of genes. Then, what controls where the genes of the second family will be transcribed, etc. for the 3rd and 4th families? If you use In Situ hybridization to locate messenger RNAs for different genes of these families, then what are some of the patterns you find? Severe mutations in these genes produce what sorts of anatomical abnormalities (give some examples.) What correlation is there between where the mRNAs of a certain gene are concentrated, relative to what part of the fly will fail to develop, or develop very abnormally if that particular gene is severely mutated? (This is a key point! Please, make sure you understand it!) What is the relation between polarity genes and the nurse cells? When is it decided (determined) which part of a fly embryo will become the anterior side, and which part will become the dorsal side? (How does that differ from the situation in frog embryos? What about human embryos?) What controls where "gap genes" will be transcribed? Mutations in gap genes cause what abnormalities? Mutations in pair-rule genes cause what anatomical abnormalities? * Why do pair rule genes fall into two different categories? Mutations in segment polarity genes have what phenotype? In Situ labeling with a nucleic acid probe with the base sequence complementary to one of the pair rule genes would have what pattern? * How might this pattern be different in a fly with a severe mutation in either one of the polarity genes or one of the gap genes? Armadillo and Hedgehog are members of which of these families of genes? Mutations in them have what phenotype? In situ hybridization labeling using base sequences complementary to them have what spatial pattern of labeling? The phenomenon of "colinearity" applies to which of the families of genes that control fly embryonic development? What sorts of phenotype are produced by homeotic mutations? Name and describe two specific examples that occur in Drosophila? If mutations in genes A and B caused homeotic abnormalities in nearby organs of flies (or any other kinds of animals), then what would you expect about the locations on that chromosomes where the DNA of those genes are located? **What is the molecular mechanism, and/or the evolutionary advantage of this geometric relation between relative locations of genes and relative locations of where those genes are transcribed? [**means, nobody knows the answer, but you should please give it some thought!] What are hox genes? What are homeoboxes? Do only hox genes have homeoboxes? (no!!) What are homeodomains? * How long are homeodomains? *Why do homeodomains contain rather large fractions of arginines and lysines? So that they can bind specifically to what? *Would you expect that re-activation of transcription of certain hox genes would be needed for regeneration of amputated structures, like arms, legs and fingers? The early cleavage stages of fly embryos differ from the equivalent stages of any species of vertebrate in what respect? Hint: would you consider the yolk syncytial layer of teleost eggs as perhaps the one slight exception to this difference? What are pole cells? Where are they formed? And what function do they serve? In theoretical science, what do people mean by "models". (hint: they don't mean people who pose for advertisements). The Positional Information model (= the morphogen gradient model) consists of what combination of assumed facts and phenomena? Contrast what Turing meant by his invented word "morphogen" versus what this word refers to in "positional information theories. Similar to the preceding question: Contrast what is meant by a "pre-pattern", as opposed to what is meant by "positional information". *If one or more mutations caused drastic changes in the locations or numbers of organs formed, but did NOT cause any change in the spatial distribution of morphogen chemicals, then that would fit in better with which category of hypotheses? *Would either category of theory expect that spatial distributions of (actual) morphogens could occur without causing changes in the structural phenotype of developing embryos? (hint: No) What is meant by polyembryony? *Could you invent some way of explaining polyembryonic development (=controlling embryonic cell differentiation) in terms of positional information? (hint: it isn't impossible). Are sharks teleosts? What else aren't teleosts, but are fish? Is embryonic development very similar in all kinds of fish? (no!) Is embryonic development very similar in all kinds of teleost fish? (yes!) *The total number of species of teleosts is about what fraction of the total number of species of all kinds of vertebrates, including those that live on land? (hint: half) Embryological research is now being concentrated on what specific kind of fish? What are the advantages of the eggs of this fish? As compared with other vertebrates? As compared with other species of teleosts? In general, what criteria are used to chose which species of plants and animals will be used as "model organisms". Can you name 3 or 4 model organisms? Who were John P Trinkaus and William Ballard? They studied the embryos of what kinds of animals? What is meant by meroblastic cleavage? As contrasted with holoblastic cleavage? Which of these patterns of cleavage occurs in the normal development of each of the following? Frogs? Salamanders? Teleosts? Reptiles? Birds? Mammals? ! What about Platypus?! Sea urchins? Sea Squirts? (Why do flies not fall in either category? **Which category of cleavage would you guess that the fly pattern of cleavage probably evolved from?) Is mammal gastrulation more similar to that in birds or that in frogs? *WHY!? Name and describe the two extraembryonic membranes that teleost fish embryos have. Name and describe the four extraembryonic membranes that embryos of reptiles, birds and mammals have. (Trick question: What parts of the body do each of these extraembryonic membranes develop into?) Another trick: What is similar about the blastopore of fish embrys and mammal embryos? "Deep cells" develop into what part of the fish's body? Describe teleost gastrulation? Describe teleost neurulation? What is "epiboly"? What is "cavitation"? What does our textbook mean by "secondary neurulation" as opposed to "primary gastrulation"? **The invention of these two terms conceals what hypotheses about the mechanism of neurulation, or of the formation of internal cavities lined by epithelia? A side issue: the amniotic cavity of mammals is formed by cavitation, but in birds it is formed by folding and fusing of two sheets of tissue. *What are some other examples in embryology, including experimental embryology, in which a certain anatomical arrangement of cells can be created by either of two or more (seemingly!) completely different processes. * In general terms, what are the key ideas of Steinberg's "Thermodynamic theory" of how cells reach the same geometric arrangements by different pathways? What is spina bifida? * Why is it medically important to improve our understanding of the mechanism(s) of neurulation? What effect does vitamin B12 have on the frequency that human babies will be born with spina bifida? Currently, about what fraction of babies are born with spina bifida? ("hint": 1 in 500) In regard to embryonic induction, what is the special meaning of the word "competence"? In regard to cell differentiation, what is meant by "determination"? Can cells differentiate without determination? (hint: no) Can determination occur without differentiation? (hint: yes) What are some specific examples? What different meanings are given to the term "stem cell"? *What is done in a bone marrow transplant? Compare that with a skin graft? (hint: please regard both these questions as being related to stem cells) **What other tissues' stem cells might be someday be transplanted into people, unless politics blocks research? (& no jokes about telencephalon transplants as a solution to these political debates.) What are neurons, axons, dendrites, growth cones, and synapses? And how are each of these related to the others. How was the research (and hypotheses) of Santiago Ramon y Cajal (in what country?) related to the research of Ross Harrison (in what country?)? How was tissue culture invented, and for what initial purpose? *This followed what other experimental attempt to test the same theory? *What were the other theories about what causes the formation of nerve fibers? Motor nerves do what? Sensory nerves do what? Which parts of which germ layers do motor and sensory nerves develop from? What is the meaning of each of the following: Chemotaxis? Haptotaxis? Contact guidance? Galvanotaxis? Neural projections? The retino-tectal connection? What are the three main subdivisions of the ectoderm? Describe the process by which they are separated from each other. Describe and name the FOUR main subdivisions of the Mesoderm? Are vertebrates the only kinds of animals that have notochords? Can you draw a notochord? What is it made of? What function does it serve? Why is it bigger than the neural tube in an amphibian larva, but much smaller than the neural tube in (embryos of what kinds of animals)? Could you draw a notochord in its geometric position relative to somites and the neural tube? *Why are they "automatically" in this geometric relation to each other? * Functionally, why are somites, notochord and neural tube in this spatial arrangement relative to each other? What parts do each somite become divided into? What is the dermis, and where do the cells come from that form the dermis? What is the myotome? From what original locations do all the skeletal (=voluntary) muscle cells of vertebrate bodies come from? *Isn't that a bit odd? *Would you expect it from Positional Information? Draw the relative geometric shapes and positions of the dermatome, myotome and the two subdivisions of the sclerotome. The anterior half of each of the vertebra (cartilages, and then bones) was formed by cells from what? What are some of the theories proposed to explain how somites become formed? Do somites continue to exist in the body, or are they only temporary in the embryo? The segmentation of what anatomical structures are controlled by the separation of the paraxial mesoderm into somites? Intermediate mesoderm forms where? What organs do intermediate mesoderm develop into? Do early embryos use the same kidneys as later embryos? After birth, do we use the same kidneys that we used during embryonic development? When the lateral plate mesoderm splits into two epithelia, what is the fluid-filled cavity between them? How do identical twins form, really? (as contrasted with what you may have been taught before) How can obstetricians deduce when the separation occurred, by looking carefully at the amnion and the chorion? In atherosclerosis, what actually causes the blockage of arteries, as contrasted with what you may have been told before? Compare the structure of capillaries, veins and arteries? Which have the thickest, and which have the thinnest walls? Which contain blood at the highest, and which at the lowest, pressures? What principle that you learned in the previous section of the course explains how capillaries can bear such strong pressures? ** In atherosclerosis, why do the extra smooth muscle cells make the inside wall of the artery bulge inward, instead of making the outer wall of the artery bulge outward? If you had a drug that could cause the latter to happen, instead of the former, what purpose could it serve?

 

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