{[ promptMessage ]}

Bookmark it

{[ promptMessage ]}

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

Info iconThis preview shows pages 1–3. Sign up to view the full content.

View Full Document Right Arrow Icon
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.
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
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 body. The fact that some of his offspring inherit this allele indicates that the cells carrying this mutation underwent germline integration. [ This is conceptually identical to the germline integration step we discussed for chimeric mice, except that in this case it was a spontaneous mutation that made some cells genetically different from the rest. ] C. The alien leaves, and returns to Earth 500 years later. She finds that all of the living
Background image of page 2
Image of page 3
This is the end of the preview. Sign up to access the rest of the document.

{[ snackBarMessage ]}