Second Set of Review Questions for Second Exam
Posted February 23, 2016
A) In the particular version of Turing's mechanism that I asked you to memorize,
B) Describe the spatial patterns produced by this combination of rules in a one-dimensional graph of the concentrations of the diffusible chemicals. C) Is Brownian motion sufficient to initiate pattern formation by this set of rules?
D) Is the resulting pattern more irregular when initiated by random variations than when initiated by regularly-spaced stimuli?
E) What are some embryological phenomena that could possibly be produced by this kind of "reaction-diffusion system", like the ones invented by Alan Turing?
F) Imagine that some cells obey the following sets of rules:
G) Imagine cells that obey the following rules:
H) Why can't Turing's and other reaction-diffusion systems explain embryonic regulation (what Driesch discovered)?
*I) Why are computer simulations useful (or necessary?) to answer such questions as whether the patterns generated can be regular, whether their wave-lengths can vary with diffusion rates or sizes of tissues where the reaction is going on? (I realize you probably have not yet experimented with such computer programs, but you have observed them in class and on web sites.)
J) Consider and compare which is more useful for understanding how genes cause embryos to form spatial patterns:
K) How could a computer program be useful for testing whether hypotheses actually predict the phenomena that they were invented to explain. (Don't the inventors of hypotheses know what they predict? Why not just ask the author of a theory?)
*L) Did you ever notice that zebra stripes are narrower around the legs, as compared with the broader stripes that encircle the main body like belts?
*M) Notice that animals with spotted color patterns tend to have rings around their tails, instead of spots. Is that a confirmation of reaction diffusion systems; or does it confirm what they predict.
*N) If developing embryos really do use reaction-diffusion systems (like those invented by Turing) to generate anatomical patterns (like pigmentation patterns), does that mean that they can only have a limited range of geometrically different patterns? In contrast, if development uses Lewis Wolpert's "positional information" type of mechanism would any such limitation be expected? hint: why not?
Maybe we have 5 fingers for reasons related to the reason echinoderms have 5 planes of reflection symmetry. Argue pro or con.
O) Did Driesch discover what amounts to dilation symmetry?
P) If so, do echinoderm embryos have this dilation symmetry? Or is dilation symmetry possessed by the mechanisms that echinoderm embryos use to break reflection and displacement symmetry?
Q) Do tensor variables have more or less symmetry than scalar variables.
R) In terms of historical dates, could Curie have met Driesch? What could they have learned from each other? (By coincidence, both got interested in occult seances)
S) Argue pro or con: Gastrulation in mammals breaks reflection symmetry? Or maybe primitive streak formation? Or formation of Henson's node?
T) Argue pro or con: Somite formation breaks displacement symmetry?
*U) Alternatively, are such embryological processes controlled by mechanisms that break symmetry?
V) What symmetries do Dictyostelium slugs and fruiting bodies have at their sequential development from chemotactic aggregation to fruiting body?
W) If small particles of plastic or carbon become stuck to the outside surfaces of crawling cells,
contrast the observed directions and amounts of transport of such particles attached to the plasma membranes of the following:
X) Describe the directions of actin movement in tissue culture cells as compared with Amoeba proteus.
Y) Argue pro or con (while demonstrating knowledge and creative imagination)
Z) How is the crawling locomotion of tissue culture cells related to the invasiveness of cancer cells?
MORE TO COME...
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