Exam_4_key - Name _ BIOLOGY 325H Genetics Spring 2010 Final...

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Name ___________________ 1 BIOLOGY 325H Genetics Spring 2010 Final Examination (160 points) Before you do anything else , please: check to make certain that your copy of the exam is complete, i.e. 9 pages. print your name legibly in the space provided at the top of every page. _______________________________________________________ 1. [16 pts] Describe in order the sequence of physiological events which allow a presynaptic action potential to produce an excitatory postsynaptic potential (EPSP) at a chemical synapse that uses acetylcholine. Be sure to name all proteins and ions that we discussed as being part of this process. 1. Action potential opens voltage-gated Ca-channels in presynaptic membrane. 2. Ca +2 ions flow down concentration gradient through channels into cytosol. 3. Cytosolic Ca +2 causes synaptic vesicles to undergo exocytosis, fusing with plasma membrane and releasing acetylcholine into the extracellular space (synaptic cleft). 4. Acetylcholine diffuses across synaptic cleft, binding to acetycholine receptor (AChR) proteins on outside of postsynaptic cell membrane. 5. Acetylcholine binding opens the ligand-gated AChR channel, permitting Na + ions to flow down concentration gradient into cytosol of postsynaptic cell. 6. Influx of Na + depolarizes the postsynaptic cell membrane, known as an EPSP.
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Name ___________________ 2 2. [20 pts] An alien space traveler visits the Earth every few centuries to study a small population of jaguars. On one of her visits, she discovers an unusual jaquar cub that has numerous large irregular patches of black fur in his coat. She sequences genomic DNA from different parts of the cub's body, and finds that the patches of black skin carry a dominant mutation (which she calls the 'black allele') in the melanocortin-1 receptor ( MC1R ) gene, whereas normally colored patches do not. She concludes that the 'black allele' is a new mutation that occurred in one nucleus when this jaguar embryo was composed of only a few cells. A. We discussed the MC1R gene in class. In general terms, what role does it play in determining coat color in jaguars and other mammals? The MC1R protein is a plasma membrane receptor which regulates the synthesis of the pigment melanin in melanocytes. MC1R activity is regulated by local hormone or growth factor concentrations, and plays a central role in determining the coat coloration of mammals. B. When the black-patched male is old enough to mate, the alien observes that some of his offspring are completely wild-type while others are solid black and carry the 'black allele' throughout their entire body. Explain this finding based on your knowledge of genetics and developmental biology. The black-patched cub carries the dominant 'black allele' in some but not all cells of his
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This note was uploaded on 09/12/2010 for the course BIO 325H taught by Professor Staff during the Spring '08 term at University of Texas at Austin.

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Exam_4_key - Name _ BIOLOGY 325H Genetics Spring 2010 Final...

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