《细菌的遗传分析》PPT课件.pptx

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1、第四章细菌的遗传分析FocusonE.coli第一节细菌的接合（Bacterialconjugation)1.TheexperimentsdonebyLederbergandTatum1940s2.TheFplasmidandconjugation(F质粒与接合）Plasmids:smallercyclesofdouble-strandDNAthatdonotcarryessentialgenesFplasmid(sexfactor,fertilityfactor)F+×F－接合，95%的F－转变为F+，染色体上基因重组频率极低TraS和Tr

2、aT编码“表面排斥”蛋白，使F+与F+细胞不能结合3.Highfrequencyrecombination(Hfr)bacteriaandthetransferofchromosomalgenes(高频重组菌株与染色体转移)Becausethetransferisusuallyinterruptedinthemidstream,thesecondhalfoftheFplasmidisnottransferred.Onlyabout1/10000Hfrcellstransfersanentirestrandofitschromosometoare

3、cipientF－cellDNAfromthedonorwillbelostunlessitisincorporatedintotherecipient’schromosomethroughadoublerecombination4.F’plasmidandsexconductionF’质粒和性导FormationofanF’plasmidmerozygoteSexconductionUsingF’plasmidforcomplementationanalysis5.SummaryofconjugationinE.coli第二节中断杂交实验与重

4、组作图InterruptedmatingexperimentandrecombinationmappingInthemid-1950sEllieWollman&FrancoisJacob1.Interruptedmatingexperimenttime(min)transferredgenes＜99azir11azirtonr18azirtonrlac+24azirtonrlac+gal+ComparisonsofinterruptedmatingstudiesusingdifferentHfrstrainsconfirmthatthebact

5、erialchromosomeisacircle2.RecombinationmappingInterruptedmatingexperimentscannotdistinguishtherelativepositionsofgeneswithinabout2minutesofeachotherandthusgiveonlyacrudeideaofgenelocation.RecombinationanalysesofHfrcrossesimprovemappingaccuracy◇Propertyofbacterialrecombinatio

6、nAsinglecrossover(oroddnumber)wouldbelethalbecausetheringisbrokentoproduceastrange,partlydiploidlinearchromosomeToproducerecombinationcells,theremustbeanevennumberofcrossovers.Onlyoneproductofrecombinationsurvives.Thereciprocalexchangeproductisgenerallylostinsubsequentcellgr

7、owth.(只有偶数次交换才能保证细菌染色体的完整性，产生平衡的有活性的重组子；重组子只有一种类型，相反的重组子不会出现）◇RecombinationmappingHfrlac+ade+Strs×F－lac－ade－Strr根据中断杂交试验，已知lac和ade紧密连锁，且lac先于ade进入F－在含有链霉素的基本培养基上筛选ade+strr，再影印到EMB培养基上检测重组子类型紫红色菌落：lac+ade+780（亲本型）白色或粉红色菌落：lac－ade+220（重组型）Donor:lac＋ade＋Recipient:lac－ade－Progen

8、yParental:lac＋ade＋lac－ade－Recombinant:lac＋ade－lac－ade＋RF(lac-ade)=lac－ade+(