Are mutations spontaneous or induced?7-11
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Luria-Delbrickfluctuation testIn1943,SalvadorLuriaand Max DelbriickToexamine the origin ofbacterial resistance tobacteriophage.Cold Spring HarborLaboratory,1940s7-12
Copyright © The McGraw-Hill Companies, Inc. Permission required to reproduce or display 7-12 Luria-Delbrück fluctuation test fluctuation test Cold Spring Harbor Laboratory, 1940s In 1943, In 1943, Salvador Salvador Luria and Max Delbrück. To examine the origin of To examine the origin of bacterial resistance bacterial resistance to bacteriophage bacteriophage
icideresistanceHypothesis1:Resistanceisaphysiological responsetoabactericide86066060606060606606060606060800000000000000028Hypothesis2:Resistancearisesfromrandommutation0600000068808204Fig.7.47-13
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Primarycultureofphage-sensitive bacteriaDilutetoapproximately103cells/ml.SinglesecondarycultureInoculatesamplesinto agarmediumcontainingphage383中?Phage-resistantcoloniesfromsamplesPhagc-rcsistant colonicsofindividualsecondaryculturesfromreplicate samplesofsinglesecondarycultureLatemutationEarlymutation
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Replica plating verifies preexisting mutations1.Invertmaster plate;pressing against2.lInvertsecondplate(replicaplate):pressingvelvetsurfaceleavesanagainst velvet surfaceimprintofcolonies.SaveplatepicksupcolonyimprintSSR-MasterplatePenicillininmediumNopenicillininmedium3.Incubateplate.VelvetReplicaplateS=penicillin-sensitive4.Onlypenicillin-resistantbacteriacoloniesgrow.CompareR=penicillin-resistantwithpositionofcoloniesbacteriaonoriainalplateFig.7.5a7-15
Copyright © The McGraw-Hill Companies, Inc. Permission required to reproduce or display 7-15 Replica plating verifies preexisting mutations Replica plating verifies preexisting mutations Fig. 7.5 a