You are given a flask with liquid media containing a population of S. pombe cell
ID: 210821 • Letter: Y
Question
You are given a flask with liquid media containing a population of S. pombe cells that have a temperature sensitive mutation of a gene that causes complete loss of function of the gene product at the restrictive temperature. The flask had been incubating at the permissive temperature before it was given to you, and the cells in the flask were replicating asynchronously with respect to the stage of the cell cycle.
The mutated gene in this strain of yeast encodes S-cyclin.
Which FACS plot (see attached figure) best represents how cells in this flask would appear following growth for 2 hours at the restrictive temperature ?
#1 #2 #3 cells in G phase #4 #5 #6 cells in Gz and Mphases cells in Sphase relative amount of DNA per cell arbitrary units)Explanation / Answer
Answer. In my opinion plot no 6 will be the most likely scenario. As we know that the mutated gene encodes S cyclin in a temperature sensitive manner. Now, if the temperature is not conducive S cyclin will not express which is the exact scenario here. If S cyclin is not expressing then all the cells in the culture will arrest at S phase of the cell cycle (S cyclin is required to move cells from S phase to M phase). As the S phase will fall in between position no 1 and 2 in the graph then it means that plot no 6 is the right answer as this is the only graph that represents all the cell population at S phase.
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