10基因突变

Chapter10Genemutations基因突变10.1Mutanttypes突变类型10.2Detection基因突变的检出10.3Mechanisms基因突变机理10.4DNARepair基因损伤的修复10.5Mutantpart突变的部位Mutation突变Excisionrepair切除修复Pointmutation点突变Directrepair直接修复Grossmutation大片段突变Nonsense无义突变Transversion颠换Frameshift移码突变Silentmutation同义(沉默)突变Missense错义突变Transition转换Mutagen诱变剂Recombinationrepair重组修复Genemutations:MutationsarealterationstotheusualDNAsequenceofanorganismthatresultfromtheactionofchemicalandphysicalagentsorerrorsofDNAreplication.Mutationsareperpetuatedbythegenotypeandphenotype.Organismsmayhavewild-typeormutantphenotypes.Pointandgrossmutationsexist.Onlymutationsinthecodingregionsofgenesarelikelytoaffectproteinfunction.10.1Genemutations基因突变：具有遗传效应的DNA分子上特定的核苷酸的序列发生改变，导致遗传效应发生相应变化。10.1.1突变类型：根据产生原因：1.Spontaneousmutation(自发突变）:在自然状态下，生物体起因不明自发产生的一类突变2.Inducedmutation（诱发突变）:经各种人为因素处理后引起的突变。根据基因突变的表型效应分：1.Morphologicalmutation（形态突变）：生物体外形可见的突变。如植株的高矮、种子的形状、翅的长短、眼睛的颜色等2.Lethalmutation（致死突变）：显性：一产生即导致个体死亡，不可能传递给后代隐性：二倍体生物中纯合时导致死亡，杂合时被掩盖，在后代中传递3.Conditionallethalmutation（条件致死突变）：改变生物体适应性的突变。4.生化突变：生物体形态未发生改变，代谢的生化过程发生了变化根据基因突变的遗传密码分：1.Samesense(orsilent)mutation（同义突变）：Mutationsmayoccuratthethirdbaseofacodonanddonotchangetheencodedaminoacid.Silentmutationshavenoeffectontheencodedproteinanddonotresultinamutantphenotype.密码子的第三个碱基突变，不改变编码氨基酸e.g.亮aaCUUCUAUUA对应的DNAGAAGATAATCUCCUGUUGGAGGACAAC2.Missensemutation（错义突变）：Thesepointmutationsinvolvethealterationofasinglebasewhichchangesacodonsuchthattheencodedaminoacidisaltered.密码子的第一、二位碱基改变导致对应的aa改变3.Nonsensemutation（无义突变）：Nonsensemutationcreatestopcodons（UAA/UAG/UGA）andproduceshortenedpolypeptides蛋白质合成提前终止，产生不完整的、无正常活性肽链4.Frameshiftmutation（移码突变）：Frameshiftmutationsinvolveinsertionordeletionofabaseproducinganalteredreadingframe.Frameshiftmutationsusuallyhaveaseriouseffectontheencodedproteinandareassociatedwithmutantphenotypes.e.g.ATGTTTCCCAAAGGGTTT---CCCTAGTACAAAGGGTTTCCCAAA---GGGATCmRNAAUGUUUCCCAAAGGGUUU---CCCUAG(终止)Pro.Met—Phe—Pro—Lys—Gly—Phe-----Pro甲硫苯丙脯赖甘苯丙-----脯增加A/TbpATGATTTCCCAAAGGGTTT-----------------TACTAAAGGGTTTCCCAAA----------------mRNAAUGAUUUCCCAAAGGGUUU----------------Pro.Met—Ile—--Ser—Gln—Arg—Val--------------甲硫异亮丝谷氨酰胺精缬----------根据基因突变的碱基类型分：1.Transitionmutation（转换突变）：基因DNA分子上嘌呤碱之间或嘧啶碱之间的变化AGTC2.Transversionmutation（颠换突变）：嘌呤碱与嘧啶碱之间的变化A/GT/C10.2基因突变的检出1.生产实践中诱变剂处理作物，后代出现变异，需要检测这些变异是否遗传变异？是显性突变还是隐性突变？e.g.纯种种子诱变处理，若F1出现与亲本不同性状，F2性状分离：3/4与F1一致,1/4与亲本一致，单株自交F3不分离株(与F1同)，为显性突变纯合株，亲本为隐性纯种dd。纯种诱变DdF1自交1DD2Dd1ddF2严格单株自交显性突变纯合株DD2DD4Dd2ddddF3若诱变后F1与亲本一致，F23/4与亲本一致，1/4非亲本即隐性突变体纯合株纯种F1Dd自交F21DD2Dd1dd（非亲本类型的隐性突变纯合株,亲本为DD）若F1新性状，F2消失，F3未出现，则为不遗传变异2.现代遗传学发展，通过直接测定多肽链上aa序列和mRNA、DNA中的碱基序列，定性定量分析分子水平上的突变10.3基因突变机理：1.Physicalmutagens(物理因素):紫外线、X、γ射线。DNA突变与射线强度成正比（波长短、能量大、穿透力强、突变厉害）X、γ射线穿透力强，直接损伤性细胞DNA紫外线危害上皮细胞，使DNA形成嘧啶二聚体，局部氢键消失，结构变形，DNA复制出错，导致基因突变Highenergyionizingradiation,suchanχ-rayandγ-rayscauseextensivedamagetoDNAmoleculesproducingstrandbreaksandthedestructionofsugarsandbases.Nonionizingradiationintheformofultraviolet(UV)lightisabsorbedbybasesandcaninducedstructuralchanges.Inparticular,UVlightcancausetheformationofstructurescalledcyclobutyldimersbetweenadjacentpyrimidines,especiallythymines.DimerizationcausesthebasestostackclosertogetherandcanresultindeletionmutationsfollowingDNAreplication.2.Chemicalmutagens(化学因素):1)碱基类似物的诱发突变：结构相似的化合物替代天然碱基引起配对出错2)碱基作用物诱发突变：碱基作用物与碱基起化学反应，改变碱基结构3)移码插入物诱发突变：吖啶类化合物的移码插入manydifferentchemicalsactasmutagens.BaseanalogssubstitutefornormalbasesduringDNAreplicationandcausemutationbyhavingalteredbase-pairingpatterns.Intercalatingagentsslipbetweenthebasesinthedoublehelix.Theycausetheinsertionofanextrabaseduringreplicationproducingaframeshiftmutation.Manychemicalmutagensmodifybases,oftenbytheadditionofalkylorarylgroupsorbyde-amination.DNAalsoundergoesspontaneousmutationbyreactionwithnormalchemicalspeciesincells.Reactiveoxygenspeciespresentinaerobiccellsalsodamagebase.烷化剂：DNA碱基上H被烷基取代，复制时错配G硫酸二乙酯G-C2H5（乙基）G-C2H5/CG-C2H5/T（GCGTTA）羟胺还原剂：C-NH2C-OHCGCTTA亚硝酸氧化脱氨作用：A-氨基H（次黄嘌呤）A/TH/CCGC-氨基UC/GU/AAT3.Biologicalmutagens(生物因素)：病毒或外源DNA生物体细胞DNA重组表型改变突变a.转导诱发突变噬菌体病毒侵染动植物病毒侵入b.转化诱发突变外源DNA受体细胞(真、原核）基因重组c.转座诱发突变1950年发现玉米胚乳颜色与9th染色体上一转入片段（Ac-Ds系统）有关。10.4DNArepair（基因损伤的修复):ThepresenceofnumerousagentsthatmutateDNAhasledorganismstodevelopextensiveDNArepairmechanisms.紫外照射受损形成嘧啶二聚体的三种修复方式：directrepairexcisionrepairrecombinationrepair1.Directrepair-Photoreaction（光复活修复）：EnzymescalledDNAphotolyasesareinducedbyvisiblelightandrepairpyrimidinedimersbybreakingthelinksthatformondimerization.嘧啶二聚体光复合酶可见光中解开，DNA分子恢复原状2.Excisionrepair(切除修复或暗修复):ThisisacomplexsystemwhichisprobablythemostcommonformofDNArepair:Initially,oneofanumberofenzymesrecognizesnucleotidesthataredamagedandmarksthemforrepair;Themarkcantaketheformofanickinoneofthestrandsofthedoublehelixadjacenttotheareaofdamage;Annucleaseremovesthedamagedbaseandadjacentbasesleavingagap.;ThegapisthenfilledwithnewDNAbyaDNApolymeraseandclosedbyDNAligase.a.内切酶识别二聚体：在二聚体一侧切开b.DNA多聚体酶Ⅰ中5’—3’外切酶从切口5’起，一个个将二聚体及附近碱基切除c.切口处以另一单链为模板，多聚酶Ⅰ作用下，5’—3’合成新互补单链d.DNAligase片段连接完成修复3.Recombinationrepair(重组修复):Recombina