ICQs13,14.ppt

13.1 The polarity of the anterior-posterior axis (i.e. which is the future head and which the future tail end) in a Drosophila embryo is first decided a) before fertilization. b) at fertilization. c) during cleavage. d) during gastrulation. e) after gastrulation. ICQs Class 13 13.2 * The polarity of the dorsal ventral axis (i.e. which is the future back and and which is the future belly side) in a Drosophila embryo is first decided a) before fertilization. b) at fertilization. c) during cleavage. d) during gastrulation. e) after gastrulation. 0.5 points The polarity of the animal-vegetal axis in a Xenopus embryo is first decided a) before fertilization. b) by the process of fertilization. c) during cleavage. d) during gastrulation. e) after gastrulation. 10-5 The polarity of the dorsal-ventral axis in a Xenopus embryo is first established a) before fertilization. b) by the process of fertilization. c) during cleavage. d) during gastrulation. e) after gastrulation. 0.5 points Mesoderm arises near the equator (in the marginal zone) of the Xenopus blastula because a) animal hemisphere cells in this region are autonomously determined to become mesodermal precursors. b) vegetal hemisphere cells in this region are autonomously determined to become mesodermal precursors. c) animal hemisphere cells in this region receive signals from underlying vegetal hemisphere cells and become mesodermal precursors. d) vegetal hemisphere cells in this region receive signals from overlying animal hemisphere cells and become mesodermal precursors. 14-1.* Activin was postulated as a mesoderm-inducing morphogen because it a) was found in the medium after incubation of animal cap cell cultures. b) was found in the medium after incubation of vegetal cell cultures. c) induced different mesodermal cell types when incubated at different concentrations with animal cap cells in culture. d) induced different mesodermal cell types when incubated at different concentrations with vegetal cells in culture. 0.5 points ICQs Class 14 14-2. The dorsalizing factors that induce formation of the organizer in Xenopus embryos a) arise at the point of sperm entry and move across the animal pole toward the organizer region. b) arise at the vegetal pole and move dorsally toward the organizer region. c) arise at the animal pole and move dorsally toward the organizer region. d) are present in ventral vegetal cells before the organizer forms. e) are present in dorsal animal cap cells before the organizer forms. 0.5 points 14-3. At fertilization, the kinase GSK3 is distributed uniformly throughout the egg cytoplasm. Just before first cleavage, where do you expect the concentration of the kinase GSK3 to be lowest? On the a) ventral side. b) dorsal side. c) vegetal side. d) animal side. e) still uniform.