E55-2009 practice exam 2

21 8 points we have discussed several examples of how

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21. (8 points) We have discussed several examples of how transitions between epithelial and mesenchymal cell states can drive (i.e. dictate or underlie) a developmental event. A. Define the ‘epithelial’ state, as opposed to the mesenchymal state (2 points). B. How does an epithelial to mesenchymal transition (EMT) initiate gastrulation in the sea urchin embryo ? In your response, state which specific cell movement is generated by this EMT. (4 points) C. Which main derivative of the ectoderm is made via an EMT? ( 2 points ): ___________________ 22. (2 points) You inject a frog oocyte with a drug that destabilizes microtubules (i.e. it prevents microtubule formation), then treat the oocyte with a sperm solution to allow fertilization and zygote production to occur. 1. Will the resulting embryo produce ventral tissues? Circle your response: yes no 2. Will the resulting embryo produce dorsal tissues? Circle your response: yes no 23. (4 points) Discovery of the organizer by Spemann and Mangold revolutionized our notions about how the early embryo was formed. Name 3 functions of the organizer: 1. 2. 3. What tissue derives from the organizer? ______________________________
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E-55, Exam 2-2009: Name Page 6 of 9 24. (12 points) You are working in a laboratory that works on studying the organizer, and you happen to isolate transcripts from a novel gene that are found in blastula-stage amphibian embryos . Below, outline how you would investigate whether this gene is operative in organizer biology. Note: each question can have multiple answers, just provide a single experiment and result to logically support the following statements. See the following example question and response: “List an experiment and resulting data to show that this novel gene is a maternal contribution to the embryo.” Experiment : look for transcripts and protein at embryo stages prior to the midblastula transition Result : see transcripts or protein encoded by this gene prior to the midblastula transition A. List an experiment and resulting piece of correlative evidence would suggest this gene is important for organizer production : Experiment: Result: B. List an experiment and resulting piece of correlative evidence would suggest this gene is important for organizer function : Experiment: Result: C. List a gain of function experiment and resulting piece of functional data that would suggest this gene is important for organizer function: Experiment: Result: D. List a loss of function experiment and resulting piece of functional data that would suggest this gene is important for organizer function: Experiment: Result:
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E-55, Exam 2-2009: Name Page 7 of 9 25. (4 points) Below is a diagram of a classic experiment performed by Spemann and colleagues: a hair loop was used to separate the amphibian zygote into two halves, such that (A) both halves received the gray crescent or (B) only one half received the gray crescent. 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
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