Review for the second hour exam, part two What kind(s) or symmetry do each of the following have? somites, motor nerves, the lens of the eye, the retina of the eye snail shells dilation, and rotational symmetry plutei larvae starfish normal plutei as compared with plutei that develop from embryos separated at the two cell stage and at the four cell stage the structure of normal flagellar basal bodies (9-fold rotational symmetry) What symmetry or combination of symmetries do each of the following have? ? A B C D E K L T U V 3 N S Z # % H I X 8 = : 0 M W * + O "Breaking" symmetry means becoming less symmetrical in some consistent way (and not becoming random). Do all embryos break symmetry several times (which is simply a fact that one can observe, whether or not anyone can discover or even imagine mechanisms by which embryos break symmetry)? True or false?: Reaction diffusion systems are (hypothetical?) mechanisms that are able to break displacement symmetry by using differences in diffusion rates to magnify tiny random irregularities in chemical concentrations. True or false?: Any stage of embryonic development that succeeds in breaking displacement symmetry must have used some kind of reaction-diffusion system to accomplish this True or false?: Locations of sperm entry are used by many species as a method for breaking what kind of symmetry. True or false?: Kartagener's syndrome is evidence that human embryos break right-left reflection symmetry by means of the normal rotational symmetry of flagellar waves. Please notice the irony that Driesch concluded that dilation symmetry of separated 2 and 4-cell embryos was evidence of control by super-natural mechanisms. (Instead of breaking dilation symmetry) ------------------------------ More questions will be added.