27. blastema analogous to the progress zone; both are highly proliferative groups of cells that provide the substrate for limb extension. 28. A. Identifiy hemangioblast-specific gene, and utilize the promoter of this gene to drive GFP or lacZ. This experiment could be done easily in zebrafish or mammals. B. Expect labeled cells on the yolk sac, and possibly on (but not necessarily) the AGM, fetal liver, and bone marrow. C. Expect labeled cells just on the yolk sac. 29. The ethical complication has to do with the origin of ES cells opposed to iPS cells. ES cells are procured by removing ICM cells from an early embryo, thereby destroying a human embryo. iPS start with cultured somatic adult cells, and experiments that transform these cells into pluripotent cells. 30. A. These are large macromolecular complexes comprised of RNA and proteins. B. turn on germ-cell specific genes, silence transposable elements, maintain pluripotency of the germ cell. C. testes cords, as the germ cells are present there. D. You might expect SDF-1 to be expressed in a path/route along endoderm, final destination being the gonadal ridge, as germ cells are induced outside the embryo proper and undergo directed migration to reach the site of the developing gonad. E. Overexpress SDF-1 mRNA (or misexpress with transgenic system) in zebrafish. If SDF-1 is sufficient to direct PGC migration, this message alone should alter the routes of PGC cells, and in this case we expect ‘confused’ migration due to the presence of ectopic ligand in places where it should not be found.
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