Download 08FirstExamKey - Biology Courses Server

Exam 1 key
1. 10 pts
self organization and self replication
2. 10 pts
Wilhelm Roux perform this "ablation" experiment to test Weismann's therory of
"determinants" and mosaic development. The results of ablating one cell of the two
cell embryo was a half embryo. This was consistent with Weismann's prediction of
localized determinants and mosaic development. The result was correct, but as we shall
see the interpretation was not. If you do the "same" experiment by separating the two
blastomeres you get a very different result---- two perfectly formed smaller tadpols!!
Hans Driesch tried a similar experiment in the sea urchin, but got dramatically different
results. If he seprated the two blastomeres he got perfectly normal development of half
sized larva. This result was NOT supportive of the mosaic model of cell fate
specification. The half embryo (1 cell of a two cell embryo) was able to "regulate" and
develop without any missing parts. This was the first compelling example of the
important developmental process of REGULATION. Think about how Driesch's and
Roux's experiments differed in design if not in intent. How would you explain the
different results? What is more compelling a positive result or a negative result?
3. 6 pts
They are cell ablation, cell transplantation, and cell isolation.
4. 9 pts
Do all cells have the same DNA? This is termed the theory of Genome Equivalence.
Ideal experimental proof of Genomic Equivalence would be to transplant the nucleus
from an adult differentiated cell into an enucleated egg. Will nuclei from all differentiated
somatic cells support normal development? If true, then the DNA in all fully
differentiated somatic cells is equivalent and the process of differentiation proceeds by
fully reversible changes to the DNA.
Late embryonic and larval nuclei support development to the tadpole stage in less than
1% of the transplantations. These nuclear transplantation experiments supported the
hypothesis of Genome Equivalent, but also suggested that the changes occurring in the
genome during development and differentiation were difficult to undo. No fertile adults
were obtained.
The question still remained: Can fully differentiated somatic cells support normal
development when transplanted into an enucleated egg?
5. 10 pts
Transgenic animal: animal that expresses a transgene; a foreign gene inserted into the
genome by using recombinant DNA and in vitro cloning techniques.
Reproductive Cloning: Using nuclear transfer and cloning techniques to generate a
genetically identical animals.
Therapeutic Cloning: Using recombinant DNA and cloning techniques to generate
genetically engineered or defined totipotent or pluripotent stems cells for treatment of
diseases, or production of tissues for transplantation.
Imprinting: It turns out that during differentiation of the gametes the DNA is specifically
altered in a sex (sperm and egg) specific way that leads to differential gene expression in
the genes of the two gametes. The term for this is imprinting and is the result of
differential methylation of the regulator regions of genes. Thus the patterns of
methylation during gametogenesis are distinct in the in the sperm and egg nucleus.
6. 10 pts
Fertilization can be divided into four main parts
1. Recognition events between sperm and egg: species specificity
2. Regulation of sperm entry into egg: block to polyspermy
3. Fusion of sperm and egg genetic material
4. Activation of developmental process within the egg
7. 15 pts
8. 10 pts
fast block to polyspermy: Increased Na current leading to depolarization within 1/10 of a
second.
Slow block to polyspermy: The cortical reaction is responsible for the slow block to
polyspermy
9. 5 pts
where, at transition of cleavage to gastrulation stage, the zygotic nucleus takes control of
the cell cycle
10. 5 pts
The blastocel spatially separates cells so they do not touch one another. Cells at the roof
of the blastocoel normally become ectoderm. If you transplant cells from the roof of the
blastocoel next to the yolky cells at the base of the blastocoel they will differentiate as
mesoderm. Mesodermal derivatives are normally produced from cells adjacent to the
endodermal precursors. One possibility that we will thoroughly explore is that the vegetal
cells “induce” via cell-cell interactions the adjacent cells to become mesodermal. Thus
the formation of the blastocoel may be necessary to prevent inappropriate "inductive"
interactions among early cells of the blastocyst. The second obvious need for the
blastocoel may be during the subsequent stage of development, GASTRULATION,
where cells migrate into the interior of the blastocoel.
11. 10 pts
jelly layer…amphibian or fish likely, external fertilization, not mammal.