Vertebrate embryology: first set of review questions
Questions that you should be able to answer.1) What is polyspermy?2) Why does polyspermy prevent embryonic development? 3) What is the fast block to polyspermy?
4) How does the fast block resemble nerve impulses? 5) What is the slow block to polyspermy? In sea urchins, what are its 3 main events? 6) What is a fertilization membrane? How is it related to the fast block to polyspermy? 7) Do sea urchin oocytes form a fertilization membrane? What about mammal eggs? 8) Do sea urchin oocytes complete both meiotic divisions before fertilization? 9) In development of mammals, including humans, how many meiotic divisions are completed before fertilization? 10) Are there any kinds of animals whose oocytes are still tetraploid until after fertilization, and then become pentaploid for a while? 11) Does the textbook have a diagram related to this phenomenon; and what did you learn from it? 12) Are human oocytes triploid for a period of time after fertilization? Why? Until what happens?
13) Draw a sketch of a mammal cleavage-stage embryo, next to a sketch of a sea urchin 8 cell stage embryo: 14) What is the morula stage of embryonic development; and where does the term "morula" come from? 15) What kind of animal has a larval stage called a "pluteus" and where does that name come from? 16) Sketch a blastula stage of a sea urchin embryo, as compared with a blastocyst stage of development of a mammal embryo. 17) Sketch the process of gastrulation as it occurs in sea urchin embryos (in a row of drawings) 18) Make sketches that show the differences of gastrulation as it occurs in sea urchins, in amphibians, in birds and in mammals. 19) Gastrulation geometrically separates the future ectoderm, from what? 20) What are the three primary germ layers? 21) The process of neurulation separates what into *the neural tube, *the neural crest and the *somatic ectoderm? 22) Are the fertilization and cleavage stages of mammal development most similar to the equivalent stages of sea urchins, frogs and other amphibians, birds and reptiles or teleost fish? In what ways? For what reasons, evolutionary or otherwise? 23) Are the blastula/blastocyst stages of mammal development most similar to the equivalent stages of sea urchins, frogs and other amphibians, birds and reptiles or teleost fish? In what ways? For what reasons, evolutionary or otherwise? 24) Is the gastrula stage of mammal development most similar to the equivalent stages of sea urchins, frogs and other amphibians, birds and reptiles or teleost fish? In what ways? For what reasons, evolutionary or otherwise? 25) What is meant by a chimera? In mythology? In embryonic development? 26) What are extraembryonic membranes? 27) What are the names and functions of the four extraembryonic membranes formed in reptiles, birds and mammals? 28) Sketch the positions of each of these extraembryonic membranes, and their anatomical connections to the animal's body. 28) Teleost fish form what two entirely different extraembryonic membranes? (Names, functions; sketch geometry) 29) If human twins are contained within the same amnion, then at what stage did the twins separate? (And please make a sketch, that clarifies your reasoning.) 30) What about if a pair of human twins are enclosed within the same chorion, but each has its own separate amnion? (And please make a sketch, that clarifies your reasoning.) 31) Conjoined twins are enclosed within which of the four extraembryonic membranes? Why are you sure of this conclusion?
Questions that you should be able to figure out an answer.a) How could you prevent the lifting of a fertilization membrane away from an oocyte surface? How? Invent a method? (Hint: osmotic pressure)b) If you soaked oocytes in a chemical that temporarily inhibited the right enzymes, how could that prevent the slow block to polyspermy from being effective? (and prevent the formation of the fertilization membrane from being visible or effective? c) Suppose there were a very low number or concentration of sperm nearby, then why would that allow normal development of some embryos, even without fast and slow blocks to polyspermy? d) Suggest several reasons why most people assume that oocytes are haploid until fertilization.
e) Fish embryologists have a clever method for creating embryos that are homozygous for all their genes. Figure out how this method works. f) Why might an embryologist want totally homozygous animals to experiment on? g) Suppose instead that you prematurely activated the blocks to polyspermy (before a sperm had fused with the oocyte) and you then inhibited the second meiotic division, how could that produce a diploid embryo?
h) The immune systems of genetically chimeric vertebrates do not make antibodies that attack the tissues that have either set of genes. i) Wolpert assumes what kind of control mechanisms decide which embryonic cells will form which particular organs?
j) Consider possible reasons why the branch points in cells' differentiated fate occur in conjunction with geometric rearrangements of future germ layers, and their subdivisions. Because of some evolutionary or ancestral conservatism? Because differences in active forces and cell shapes are the triggers that control how cells will differentiate? Because the first differences in gene expression (protein synthesis) to occur in gastrula and neurula stage embryos include different specific cell-cell adhesion proteins?
|