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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.