E55-2009 practice exam 2

Does this experiment demonstrate that the gray

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Does this experiment demonstrate that the gray crescent is essential for dorsal structures? Circle the best answer to this question: YES NO MAYBE In 1-2 sentences, briefly provide your reasoning: 26. (8 points) A new cadherin gene is isolated from zebrafish ectoderm at the end of gastrulation. Knockdown of this cadherin with morpholinos results in normal brain and spinal cord development, and normal epidermis. Interestingly, researchers notice that the jaw structures in the morpholino-injected embryos look abnormal, and they also observe that the heartbeat is irregular, with blood flow in the cardiac outflow tract appearing to be restricted. A. Based on these data, propose a hypothesis as to the role of this gene in ectoderm development. Hypothesis: B. Name one piece of data that would provide correlative support for your hypothesis. C. Name one piece of data that would provide functional support for your hypothesis.
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E-55, Exam 2-2009: Name Page 8 of 9 27. (4 points) In a classic episode of the X-files entitled “Postmodern Prometheus,” an evil developmental biologist is experimenting with a human Hox gene most similar to the Drosophila homeotic gene proboscipedia . Mulder is unfamiliar with homeotic genes, and asks for an explanation from Scully, who does her best to remember her undergraduate biology classes. Name three key features of homeotic genes that Scully should enumerate to Mulder: Feature #1: _______________________________________________________________ Feature #2: _______________________________________________________________ Feature #3: _______________________________________________________________ Next, Scully is asked by Mulder to assign the function of the vertebrate orthologue of proboscipedia , Hoxa2 . To generate data rapidly, she performs a morpholino knockdown in zebrafish. She finds that the zebrafish embryos are totally normal. While she is puzzled by this result, as an episode-viewer trained in developmental biology, you are not surprised—in 1-2 sentences , explain why. 28. (4 points) You transplant a Nieuwkoop center from a donor frog embryo to the ventral side of a host frog embryo, placing it in the ventral endoderm of the host. Based on your knowledge of the function of the Nieuwkoop center, predict the outcome of this experiment. In 1-2 sentences, state what affect the Nieuwkoop transplant will have on the host tissues, and describe the overall body plan of the embryo after organogenesis is completed. 29. (4 points) List two features of the cleavage period. 1. 2.
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E-55, Exam 2-2009: Name Page 9 of 9 30. (10 points) The accumulation of B-catenin is a key step in the progressive specification of dorsal structures in amphibian embryos, that leads to the formation of the organizer. Recall that chordin is a molecular marker of the organizer. A. (6 points) For each of the experimental situations below, indicate the localization of B-catenin at the blastula stage by/shading in the provided diagram. Indicate the expected level of chordin expression using the classification: High=higher than normal; Normal; Low=lower than normal. Treatment None (normal, wild- type embryo) 1-cell embryo injected with large quantities of constitutively active GSK3 1-cell embryo injected with large quantities of activated disheveled B-catenin localization (draw in diagram, indicating D/V) chordin expression (High, Normal, Low) B. (4 points) In 2-3 sentences, summarize how the organizer is formed: what signal(s) contribute to organizer formation, and where does this occur in the amphibian blastula? You *may* use a diagram to explain your answer.
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Does this experiment demonstrate that the gray crescent is...

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