Embryology Biology 441 Spring 2007 Albert Harris and Andrius Masedunskas


Review Questions for third Exam

You should be able to recognize special vocabulary terms, and also pictures which are posted on some the web sites for this section of the course, including Limb Bud Development, Developmental Mechanisms, Cellular Slime Molds, Cancer, Neural connections, Extraembryonic Membranes, and Sex Determination.

What different organs do vertebrate limb buds develop into? [For example, in fish, birds, snakes, etc.]

Vertebrate limb buds often react to surgical experiments in much the same ways as Driesch discovered in whole embryos of echinoderms: Describe some examples.
How can you cause a vertebrate embryo to develop with two complete hearts?
Compare the formation of the single heart and the single uterus in humans.
Other than grafting an extra limb bud to a developing vertebrate embryo, how can you cause an embryo to develop an extra (fifth) leg? Using only chemicals, what is another way to cause formation of a fifth leg?

Name the three geometric axes of the body, and all its organs, such as limb buds.

Vertebrate limb buds start out with what symmetry? (you can draw them if you want to)
What happens if you cut off an early limb bud, and graft it back with its dorso-ventral and anterior-posterior axes reversed (i.e. upside down and backwards)? [Hint: what happens depends very much on how early in development you carry out this operation, and there can be three different results depending on when you do the operation].
What other organs of the body have been subjected to this same kind of grafting experiment, turning the early organ rudiments upside down and backwards?

What is the AER? Where is it located? What organs or parts of organs develop along the location of the AER?
Surgical removal of the AER causes what abnormality in a developing embryo? [Hint: depending on when this removal is done!]
Who discovered this effect of removing the AER from an early embryo? [Name of the scientist].
Draw a picture of the AER, as seen in a histological cross section, first in a bird embryo, and second in a mammal embryo.
Does any comparable structure develop where fish are going to form fins?
Grafting a second AER to a limb bud causes what sort of abnormality in subsequent development?
Which of the 3 primary germ layers does the AER develop from?
What is different about the AER of newts and other salamanders, and also snakes?

The determination of the proximo-distal axis of vertebrate limb buds is controlled by cells of the ZPA (which stands for what?), and how was this discovered?
What abnormality can be induced in limb buds using the chemical retinoic acid (which is a form of vitamin A)?
How can you get one or more extra feet to develop where the tail of a frog should be?
What role does the signaling protein called "sonic hedgehog" apparently serve in leg and wing development?
What comparable role is played by proteins of the Wnt family?
What is apoptosis? How would your hand be different if apoptosis had failed to occur during your embryonic development?
How might you use apoptosis as the basis for a new kind of cure for cancer?
How might you use apoptosis to cure autoimmune diseases?

The word "morphogen" means what in "pre-pattern" type theories of embryonic development?
Contrast the meaning of this word "morphogen" by advocates of "positional information" types of theories of embryonic development.

What are "reaction-diffusion systems"? What do they produce?
What are Liesegang rings? How are they analogous to the pattern-generating mechanism(s) invented by Alan Turing, and which Hans Meinhardt used as hypothetical explanations for sea-shell patterns?

In addition to prepatterns and positional information, describe a third category of embryonic pattern-generating mechanism that was proposed by D'Arcy Thompson.
What discoveries were made by David Stopak and others that support this third category of embryological mechanism?

Cellular slime mold amoebae (especially Dictyostelium discoideum) are useful for research of what four different phenomena, that all also occur in animal embryonic development?
Describe four stages in the life cycle of this species?
Who was Kenneth Raper, and where was he an undergraduate?
What is meant by the "slug" stage of development of Dictyostelium?
What was the original evidence that aggregation by starved D. discoideum amoebae is by chemotaxis? What additional experiments by John Bonner then proved that chemotaxis must be occurring?
Was it first necessary to identify their chemotactic attractant substance as cyclic AMP, in order to prove that chemotaxis actually occurred?
Was is possible to learn what chemical this species uses for chemotaxis, without first doing experiments that they use chemotaxis? [Hint: no]

Describe the extreme capability for embryonic regulation of Dictyostelium slugs, stalks and spore masses.
Draw an aggregated hemisphere of amoebae, a slug, a stalk, and a spore mass. What are the surface curvatures of each of these?
Draw the directional amounts of surface curvatures on the surfaces of each of these, using a bunch of arrows radiating in 8 or 10 different directions from a point on their surface.
What symmetry does each stage of development have, and what changes in symmetry (if any!) occur at each stage of development?
Explain why the dilation symmetry between slugs of different sizes is related to the high degree of regulation in this species (if you believe that it is so related; otherwise, feel free to argue against this relation between dilation symmetry and regulative development.)

Cancer cells differ from normal cells in what ways? (hint: NOT growth rate or active locomotion)
What is meant by "contact inhibition", and how is this phenomenon hypothesized to be related to the more invasive locomotion of many cancer cells?
The papilloma virus vaccine recently put on sale (for about how many dollars per person) is not a vaccine against cancer, but rather...?

What are carcinomas? What are sarcomas? What are lymphomas? What is meant by leukemia?
What are teratomas, and how are the somewhat analogous to neuroblastomas?
What is metastasis?
By what criteria of shapes of cells and parts of cells do pathologists distinguish (in histological sections) whether a lump of tissue found in a person's body is malignant or benign?

Draw a cancer cell. Draw a non-cancerous cell of the same original kind.
Draw and describe the locomotion and surface movements of cancerous cells, as compared with equivalent non-cancerous cells.
Describe the experiment shown in a movie in class which indicates that cancerous cells tend to exert weaker traction forces when crawling, as compared with equivalent non-cancerous cells.
Describe 4 different kinds of drugs that are used for cancer chemotherapy, and how they are supposed to be able to kill cancer cells selectively (without also killing too many normal cells).

What are some paradoxical aspects of the effects of these chemotherapy drugs?
What essential goal does cancer chemotherapy need to accomplish? [hint: kill more cancer cells? kill fewer normal cells? something else? some combination?]
Name and describe 4 or 5 specific oncogenes, including in your description the normal functions of the proteins that these genes code for.
Why would it not be possible to avoid cancer by eliminating these genes from your genome?
What percentage of the American public dies of cancer, on the average?
Invent 4 or 5 new kinds of cures for cancer, and describe how they would work.

What are antibodies? What specific differentiated cell type makes and secretes antibodies?
What is a T-lymphocyte, and what does it have on its surface that are analogous to antibodies?
What is meant by an "antigen", and what part of an antibody molecule does it bind to?
How are allergies related to the immune system?
What are autoimmune diseases? What are three or four specific examples of autoimmune diseases?
The immune system depends on what two (related) processes that occur during embryonic development?
What is very strange and special about the DNA that codes for antibody binding sites and the binding sites of T-lymphocyte receptors?

SOMEWHAT DIFFICULT THOUGHT QUESTION: If you took a nucleus from a B-lymphocyte, and injected it into an enucleated oocyte, and implanted this oocyte into a uterus, and it developed into an animal, then why would that animal make antibodies only against one particular antigen? (This has actually been done!)

What is NOT known about the "self-tolerance" mechanism?
What has gone wrong in people who suffer from allergies or autoimmune diseases?
Why do we need an immune system?
What two differentiated cells do the attacking, against germs? Do either kind ever attack anything other than germs?
Why can't Darwinian evolution eliminate the genes for binding sites that fit "self" antigens?
In what respects is the development of each individual person's immune system logically the same as the Darwinian evolution of all the many species of animals?
How does the generator of diversity work?

Where does the thymus develop? What did people mean by saying that it was vestigial? Were they correct?
What is peculiar about "Nude mice"?
What examples of embryonic induction (in Spemann's sense of "induction") occur in the development of the immune system?
Embryos that develop from fused embryos (that were genetically different, or even of different species) do or do NOT make immune attacks against the genetically different tissues?
What do embryologists mean by a chimera? Could chimeras develop if the immune system really worked by detecting "non-self" tissues? [You are welcome to argue either pro or con].

THOUGHT QUESTIONS: If you could control the tolerance mechanism (however it works), how could that help you cure allergies? ...cure autoimmune diseases? ....help cure cancer? ...help allow organ and tissue grafts from genetically-different people?
Which is more surprising: 1. That some people get autoimmune diseases 2. That not everyone gets autoimmune diseases? 3) That differentiation of both kinds of lymphocytes is induced by outpocketings of certain parts of the endoderm? 4) That arguments about whether natural selection can produce evolution never discuss the role of natural selection (within each person's body, during embryonic development) in the formation of that person's immune system?

What are axons? What are nerve growth cones? Draw and describe their movements
How long are your longest axons? About how long are the axons of ganglion cells?
What parts of your nervous system develop from neural crest cells?
Draw the relative positions of ganglion cells, rod and cone cells, and pigmented retina cells, in the eye?
How does this geometric arrangement differ from how you, as an intelligent being, would have designed the eye and retina?
What is the optic nerve? (It consists of axons of what cells, extending to synapses in what part of the brain?)
What is the retino-tectal projection?
What is a neural projection, in general?
Are some neural projections sensory, and others "motor"? (yes).
What is meant by "motor" nerves?
What surprising result was discovered when an extra eye was surgically implanted on the side of a frog's head, and developed an extra optic nerve connecting to the frog's brain?

What are extraembryonic membranes?
What is the chorion? What is the amnion? What is the "bag of waters? What is the yolk sac?
Where does the allantois develop? What fluid gets stored inside the allantois?
What kinds of animals have enveloping layers and yolk syncytial layers?


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