LS4 Lect_9

LS4 Lect_9 - 2/1/10 ra- X rb- 94% large 6% small 1 Host...

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2/1/10 1 r a- X r b- 94% large 6% small 1 Host Range Mutants h + (wild type) can grow on E. coli s but not on E. coli r . h can grow on both E. coli s and E. coli r . 2
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2/1/10 2 Recombination in phage r + h - X r - h + Phenotype Inferred genotype Clear and small r + h - Cloudy and large r - h + Cloudy and small r + h + Clear and large r - h - Cross r - h + r + h - r + h + r - h - r a- h + X r a+ h - 34.0 42.0 12.0 12.0 3 What is map distance between r a and h? A.6 mu B.12 mu C.24 mu D.34 mu E.48 mu
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2/1/10 3 Recombination in phage r + h - X r - h + Phenotype Inferred genotype Clear and small r + h - Cloudy and large r - h + Cloudy and small r + h + Clear and large r - h - Cross r - h + r + h - r + h + r - h - r a- h + X r a+ h - 34.0 42.0 12.0 12.0 r b- h + X r b+ h - 32.0 56.0 5.9 6.4 r c- h + X r c+ h - 39.0 59.0 0.7 0.9 5 Draw the map as best as possible. How did they get the T2 host range mutants? 1st- Isolate E. coli strain resistant to T2 SELECTION- only E. coli s mutated to E.coli r will survive and grow. 2nd- plate millions of wild type T2 phage on E.coli r , the few plaques that grow will have h - mutations. 6
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4 1X10 9 pfu/ml 1X10 3 pfu/ml 1X10 9 pfu/ml 3X10 3 pfu/ml 5X10 7 pfu/ml 1X10 9 pfu/ml 7 LYSOGENY λ (lambda) makes cloudy plaques but λ repressor - makes clear plaques. Why? h + make cloudy plaques on a mixed lawn of E. coli r + E. coli s cells because it kills some of the cells but not all of them. Temperate phage (like λ ) make cloudy plaques because they kills some of the bacteria but not all of them. Some of the bacteria become immune to infection because they become lysogenic. A λ repressor - phage cannot make the repressor, therefore it cannot go into the lysogenic life cycle. This forces it to go 100% into the lytic life cycle. This kills all of the cells in the plaque making it a clear plaque. The repressor mutation is known as a virulent mutation. 8
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LS4 Lect_9 - 2/1/10 ra- X rb- 94% large 6% small 1 Host...

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