E55-2009 practice exam 3

A the heart forms from two initially separate

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A. The heart forms from two initially separate primordia. B. The heart forms from a sheet of cells that invaginates to make a tube. C. The blood forms exclusively from sheets of cells in the anterior lateral plate. D. The vessels form exclusively from sheets of cells in the anterior lateral plate. E. none of the above ______19. A mouse knockout for Fgf10 would be expected to result in: A. conversion of all appendages to a hindlimb identity B. halt of limb bud outgrowth C. failure of limb bud formation D. absence of posterior digit identities in the limb E. absence of anterior digit identities in the limb ______20. Stem cells are characterized by: A. the ability to produce numerous differentiated cell types B. the ability to self-renew (produce more of themselves) C. they are visibly undifferentiated D. they have been located in adult organs E. all of the above
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E-55, Exam 3-2009: Name Page 5 of 9 Short answer (point values indicated) . Provide a concise response in the space provided. 21. (12 points) Limb growth and patterning are closely intertwined, and the AER is a key signaling center in this series of events. Several stages of forelimb extension are shown below (labeled 1-4). Forming bony elements are depicted in gray, with their anatomical names labeled in the complete limb (stage 4). A. Label the AER in stage 1. Then, in the space below define the AER : what cells comprise it, and how would these cells appear if you looked at a three-dimensional limb bud during stages 1-3 shown above? B. Based on the known role of the AER, list what bony elements will form if the AER is removed at the following stages: Stage 1: _________________________________________ Stage 2: _________________________________________ Stage 3: _________________________________________ C. Describe an experiment that would rescue the effect of removing a Stage 1 AER, but would not require a graft of cells with ‘AER activity.’ D. You remove the AER of a stage 3 limb, and then graft the AER of a stage 1 limb in its place. What will happen? In your answer, clearly state which bony elements of the limb will form. What does this result tell us about the information provided by the AER ?
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E-55, Exam 3-2009: Name Page 6 of 9 22. (6 points) Before discovery of the true signal that operates in limb development anterior-posterior patterning, retinoic acid was a leading candidate. Retinoic acid is a small molecule compound derived from Vitamin A. When retinoic acid is soaked onto a charged plastic bead and implanted into the anterior region of a young limb bud, the fully developed limb formed mirror image duplications of the digits. A. Based on this result, retinoic acid is a candidate for the activity of which signaling center in the limb?
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A The heart forms from two initially separate primordia B...

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