Scott_Handout6-Key - 3/8/2010 MCB 104; Handout #6 Answer...

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3/8/2010 MCB 104; Handout #6 Answer Key 1. You have a mixture of Neruospora , some of which are auxotrophs and some of which are prototrophs. How can you quickly isolate the prototrophs? How could you identify the auxotrophs? Grow them on minimal media. Prototrophs survive. Auxotrophs die. To identify auxotrophs, culture individual clones in rich media, and then inoculate minimal media. Auxotrophs will grow in rich media, but not in minimal. 2. You are studying a haploid organism that lives in a vending machine. In this organism, you are analyzing the biosynthetic pathway that produces a “nutrient” called “cheez.” You isolate five distinct mutants (chz-1, chz-2, chz-3, chz-4, and chz-5), none of which is able to grown in the absence of cheez. You discover that some of the chz mutants are able to grow in cheez free media if you back certain other nutrients: (+ = growth, - = no growth): Media chz-1 - chz-2 - chz-3 - chz-4 - chz-5 - minimal - - - - - minimal + cheez + + + + + minimal + yellow #5 - - - - - minimal + orange stuff + - + + - minimal + viscous stuff - - + - - minimal + salty stuff + - + + + minimal + oily stuff + - + - - A. Why is it easier to do your mutagenesis in haploid organisms? What is the order of intermediates in the biosynthetic pathway? Which chz enzyme mediates each step? Mutagenesis in diploid organisms will typically only generate a mutation in one homolog of a gene while the other homolog remains wild-type and provides sufficient gene function. Thus, it is difficult to recover recessive alleles in diploids. In haploid cells do not have this problem. yellow #5 –(chz-3) viscous stuff –(chz-1) oily stuff –(chz-4) orange stuff –(chz- 5) salty stuff –(chz-2) cheez B. You make a chz-4; chz-1 double mutant, and grow it on minimal media + yellow #5. What intermediate compound will accumulate? Which gene is epistatic to which other gene? viscous stuff will accumulate; chz-1 is epistatic to chz-4. C. You make a chz-2; chz-5 double mutant and grow it on minimal media + yellow #5. Which intermediate will accumulate? Which gene is epistatic to which other gene? orange stuff will accumulate; chz-5 is epistatic to chz-4. 3. You perform a screen in C. elegans , and identify five different uncoordinated mutants (the mutants move in a clumsy, uncoordinated way): unc-A unc-B,unc-C unc-D, unc-E, unc-F). The C. elegans community is very good about sharing resources, and you share your unc mutants with your colleagues.
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3/8/2010 MCB 104; Handout #6 Answer Key A. A scientist at Stanfurd wants to know if these unc mutations compliment each other. She invites them to a party, and monitors their conversation.
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This note was uploaded on 04/05/2010 for the course MCB 104 taught by Professor Urnov during the Spring '09 term at University of California, Berkeley.

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Scott_Handout6-Key - 3/8/2010 MCB 104; Handout #6 Answer...

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