遗传学新版课件 12

CHAPTER12TheProkaryoticChromosome:GeneticAnalysisInBacteria1.AGeneralOverviewofProkaryotes

Afamilytreeoflivingorganism

Bacteria---Escherichiacoli

Coloniesonsolidnutrient-agarplatesSuspensioninaliquidmediumEcoli

TheBacteriaGenomeAcircleofdouble-strandedDNA

ThechromosomalDNAcanberepresentedasthehelixorasaring

Thetechniquesusedinbacteriaresearcha.Replicaplating

b.Treatmentswithmutagens

c.EnrichmentPenicillinenrichmentforauxotrophicmutants

d.Testingforvisiblephenotypes

TransposableelementsinbacteriaIS---insertionsequenceTn---transposon

ReplicationoftheEcolichromosome

SmallercirclesofDNAthatdonotcarryessentialgenesAmp---ampicillinCm---chloramphenicolKan---kanamycinHg---mercurySm---streptomycinSu---sulfonamideTet---tetracycline

Plasmids:2.GeneticExchangeinBacteria

a.Transformation:theprocessbywhichadonorDNAmoleculeistakenupfromtheexternalenvironmentandincorporatedintothegenomeofarecipientcell.b.Conjugation:theprocessbywhichbacterialcellsmakeeffectivecontactwitheachotherandDNAistransferredfromonecell,thedonor,totheother,therecipientcell.c.Transduction:theprocessbywhichDNAistransferredfromonebacterialtoanotherbyabacterialvirus.

Threeparasexualprocesses

TheU-tubeexperiment

a.BacterialtransformationAdonorDNAmoleculeistakenupfromtheexternalenvironmentandincorporatedintothegenomeofarecipientcell.

Recombination

Integration

Themechanismoftransformation

b.Conjugation

TheclassicLederbergandTautomexperiment

ConjugationF+xF-

Conjugation

HfrXF-

conjugation

Mappinggenesbyinterruptedmatingexperiments(WollmanandJacob,1956)

OrderoftransferofgenesindifferentHfrstrains

Mappinggenesusingathree-pointcross

F’plasmids

Comparingtheconjugational

cyclesofF+,HfrandF’cellsInanF+cellInanHfrcellInanF’cellBeforeconjugationEventsofconjugationafterconjugation

SomeofthesitesofF-factorintegrationintheE.colichromosome

ThesitesofF-factorintegrationc.Transduction:

Lyticandlysogenicmodes

GeneralizedtransductionMappinggenesbycotransductio