Biology 441, Spring 2013 Review for Second Hour Exam


You should be sure to know what subdivision of which germ layer each of the following develops from For example Lens develops from somatic ectoderm, more specifically from a placode.

    Pigmented retina Develops from neural tube ectoderm. Sensory retina
    Olfactory nerves
    Semi-circular canals
    Spinal cord
    Skeletal muscles Develop from myotomes of somites, paraxial mesoderm
    (Reptile) scales
    Heart Lateral plate mesoderm
    Adult kidney Metanephros; posterior part of intermediate mesoderm
    Motor nerves Neural tube ectoderm
    Sensory nerves Neural crest ectoderm
    Schwann cells
    Postganglionic autonomic nerves Neural crest ectoderm
    Facial Skeleton Neural crest ectoderm
    Skeleton in the rest of the body Sclerotome off somites, and also lateral plate mesoderm
    Pituitary gland Partly from stomodeal, somatic ectoderm.
    Salivary glands Most are endoderm; one pair may be stomodeal ectoderm.
    Thyroid gland Endoderm
    Lungs Endoderm (plus some mesodermal mesenchyme)
    Liver Endoderm (plus some mesodermal mesenchyme)
    Pancreas Endoderm (plus some mesodermal mesenchyme)
    Intestine Endoderm (plus some mesodermal mesenchyme)
    Stomach Endoderm (plus some mesodermal mesenchyme)
    Capillaries, veins, arteries Mesoderm (mostly or all from lateral plate mesoderm)


What symmetries do each of the following have? And for each one, name something else, NOT on the list, that also has that same symmetry or combination of symmetries.

    A centipede
    A four bladed propeller
    A plaid piece of cloth
    The color pattern of a Copperhead snake
    A snail shell
    A frog egg before it is fertilized
    A human embryo before it has formed its inner cell mass
    A human embryo after it has formed its inner cell mass, but before a primitive streak has developed
    A human embryo that is developing into identical twins
        (Don't forget that there are three very different ways in which identical human twins develop)
    A gastrulating or a neurulating embryo
    Teeth in a mammal's mouth (difficult, but you can figure it out)
    The individual vertebrae of your backbone
    An individual Dictyostelium slug
    An aggregating mass of Dictyostelium amoebae
    A Dictyostelium fruiting body
    Many Dictyostelium fruiting bodies, of different sizes, as compared with each other
    The mechanism that controls the relative dimensions of fruiting divisions
    The letter A
    The letter N
    The letter H
    The symbol %
    The symbol *
    A zig-zag line
    A pluteus larva
    A starfish
    Microscope lenses
    (Old fashioned) balances for weighing things
    Wheatstone bridge electrical circuits for measuring small differences in electrical resistances
    And why do they have this symmetry?
        (Don't worry if you haven't had physics, or have forgotten about Wheatstone bridges; but it's no accident they are symmetrical, and I hope you will think about it.)
    Cumulus clouds in the sky
    The graphs of any equation in which x only occurs as x squared, x to the fourth, or x to other even powers?
    The graphs of any equation in which x only occurs as x cubed, x to the fifth power, and simply as x?
    The graphs of any equation in which both x and y only appear squared, or to the fourth power.
    The graph of x times y is equal to a constant?
    In general, how are the symmetries of x and y in an equation related to the symmetry of the graph of an equation? Relate this to Weyl's definition of symmetry.
The mathematician Weyl invented the best definition of symmetry, that implies methods or criteria for inventing new kinds of symmetry. Put his definition in your own words. Or in Richard Feynman's words "A thing is symmetrical IF, there is something you can do to it (rotation, reflection, magnification, displacement by a certain distance, etc) After which it looks the same as it did before"

Argue pro or con: Driesch discovered that whatever mechanisms control pluteus formation, these mechanisms have dilation symmetry.

Argue pro or con: Embryonic development depends on many mechanism that reduce/increase symmetry.

Argue pro or con: Any completely deterministic system keeps whatever symmetry it started with. It can only become less symmetrical by means of some external signal, or by becoming sensitive to random fluctuations, like Brownian movement.


    Cilia and flagella have 9 fold rotational symmetry, but do not have any planes of reflection symmetry.

    Their lack of reflection symmetry (in flagella) is related to the asymmetry of the heart and stomach.

    >Most people with Karteganer's Syndrome have a mirror-image reversal of their aorta, heart, stomach etc. that looks perfectly normal when looked at in a mirror.


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