三年级二学期遗传学大课2principles of clinical cytogenetics

Post-TranslationProcessingPost-translationalmodifications:肽链从核蛋白体释放后，经过细胞内各种修饰处理成为有活性的成熟蛋白质的过程。Primarytranslationproductisfoldedandbondedintoaspecificthree-dimensionalstructure.Twoormorepolypeptidechainscombinetoformasinglematureproteincomplex.CleavageoftheproteinTheproteinproductsmayalsobemodifiedchemicallySTRUCTUREOFHUMANCHROMOSOMESCompositionofChromatinDNAProteins(histonesandnonhistone)Thebasicstructureunitofchromatin:

NucleosomeH1,(H2A,H2B,H3,H4)2(H2A,H2B,H3,H4)ORGANIZATIONOFTHEHUMANGENOMESingle-copyoruniqueDNARepetitiveDNASingle-CopyDNASequencesOnceorafewtimes/agenomeShortstretches(≤severalkb)Codingportionofgenes:asmallproportionofallthesingle-copyDNARepetitiveDNAFamiliesDefinition

HundredstomillionsoftimesinthegenomeRole

MaintainchromosomestructureCategoryClusteredrepeatedsequencesDispersedrepeatedsequencesPrinciplesof

ClinicalCytogeneticsYuxiaYangDepartmentofMedicalGenetics,PekingUniversityHealthScienceCenterIntroductiontoCytogeneticsCytogenetics（细胞遗传学）MedicalCytogeneticsClinicalCytogeneticsClinicalIndications

forChromosomeAnalysisProblemsofearlygrowthanddevelopmentStillbirthandneonataldeath.（死产、新生儿死亡）Fertilityproblems.（生育问题）Familyhistory（家族史）Neoplasia（肿瘤）Pregnancyinawomanofadvancedage（高龄孕妇）IntroductiontoCytogeneticsClinicalindicationsforchromasomeanalysis

Cytogenetics:thestudyofchromosomesandtheirabnormalitiesiscalledcytogenetics.TheHumanKaryotypeThechromosomesareclassifiedinto7groups(A-G)Karyotype：是指一个体细胞中的全部染色体，按照大小、形态特征顺序排列所构成的图像Centromere(primaryconstriction)、p(shortarm)、q(longarm)GbandingAchromosomeatmetaphase

chromatid染色单体

chromatid＋

＝1chromosome

p

qTelomere（端粒）telomereCentromere（着丝粒）(primaryconstriction)topa,b:metacentric（中央着丝粒）c,d:submetacentric（亚中着丝粒）e:acrocentric（近端着丝粒）f:telocentric（端着丝粒）ChromosomeIdentificationIdentificationofHumanChromosomesstained

Auniformsystemofchromosomeclassification－ISCN(AnInternationalSystemforHumanCytogeneticNomenclature)（人类细胞遗传学国际命名体系）ISCN规定的界标：着丝粒、端粒、明显的带ArmRegionBandSub-bandXq13ANormalmaleKaryotype:46,XYAnormalfemalekaryotype:46,XXChromosomeIdentificationGBanding:trypsin(胰蛋白酶)

、Giemsa(姬姆萨)QBanding:quinacrinemustard(喹吖因氮芥)

RBanding:specialtreatmemt(heating)、staining、thereverseofGorQbandingGBandingQBandingRbandingIdeogramshowingGbandingpatternsforhumanchromosomesatmetaphaseChromosomeIdentificationCBanding:stainingthecentromericregion、otherconstitutiveheterochromatinregionsHigh-ResolutionBanding:chromosomesstainedatthestageofprophaseorprometaphase,detectingasubtlestructuralabnormality(前中期、晚前期的单倍染色体带纹数可达550--850条带;典型中期染色体，一套单倍染色体带纹数约320--400条带)CBandingHigh-ResolutionBandingFluorescenceInSituHybridization(FISH:荧光原位杂交)Principles:

LabelingprobewithafluorescentdyeDenatureoftheprobeandmetaphase、prophaseorinterphasechromosomesHybridization

VisualizingthelocationofhybridizationunderafluorescencemicroscopeChromosomeIdentificationProbes:threetypesgene-specificorlocus-specificprobes（单拷贝）

repetitiveDNAprobes(satelliteDNAprobes)（重复序列）chromosomepaintingprobes(probesforentirechromosomesorchromosomearms)（染色体涂染）Asingle-copyDNAprobespecificforthefactorVIIIgeneontheXchromosomeMetaphase：中期Interphase:间期ArepetitivealphasatelliteDNAprobespecificforthecentromereofchromosome17MetaphaseInterphaseAwholechromosome“paint”probespecificfortheXchromosomeMetaphaseInterphaseApplication:toexaminethepresenceorabsenceofaparticularDNAsequencetodiagnosetheexistenceofanabnormalchromosomenumberinclinicalmaterialtodetectchromosomerearrangementswithcombinationsofFISHprobes18-yellow

Y-green

X-red23,Y;23,X24,XX24,XYHumanSpermnormaln+1n+113-green

21-red18-aqua

X-green18-aqua

X-green

Y-redPrader-Willisyndromedemonstratingdeletionof15q11-q13Green：alphasatelliteDNAatthechromosome15centromereRed：SNRPNgeneAzoospermiarelatedtoanunusualkaryotype,45,XY,-13,-19,+der(19)t(13;19)(13q12;19p13)---JournalofAppliedGenetics

一例男性不育患者核型的确定ABC1319Spectralkaryotyping(SKY：光谱核型分析)ChromosomeAbnormalitiesAbnormalitiesofChromosomeNumberAbnormalitiesofChromosomeStructureAbnormalitiesofChromosomeNumber

EuploidVariation：以染色体组为单位发生的染色体成倍的增减,2n+n=3n;2n+2n…

AneuploidVariation：细胞内染色体数目增加或减少一条或几条,2n+1;2n+2…Haploid(n)Euploid（整倍体）

Triploid(三倍体)

Definition:3nReason:dispermy(双受精)

(mostcommon)、digyny(双雌受精)Phenotypicexpression:paternal-abnormalplacenta;maternal-abortionkaryotypes:69,XXX;69,XXY;69,XYYdispermydigynyTetraploid(四倍体)Definition:4nReason:endoreduplication(核内复制),endomitosis(核内的有丝分裂)

Karyotypes:92,XXXXor92,XXYYEuploid（整倍体）Aneuploidy（非整倍体）Trisomy

（三体性）Definition:atrisomiccellinvolvesasingleextrachromosome;thatis,thecellhasthreecopiesofaparticularchromosomesandtwocopiesofotherchromosomes.Atrisomiccellis2n+1Example:trisomy21(karyotype:47,XX/XY,+21)Monosomy

（单体性）Definition:amonosomiccellinvolvesalossofasinglechromosome;thatis,thecellis2n-1.Example:Turnersyndrome(Turnersyndromekaryotype:45,X)Mechanism-

nondisjunctionMeioticnondisjunction

（减数分裂不分离）Mitoticnondisjunction

（有丝分裂不分离）MeioticNondisjunctionMitoticNondisjunction46464646464745nondisjunctionmitoticnondisjunction-mosaicismAbnormalitiesofChromosomeStructureMechanism:chromosomebreakage、reconstitutioninanabnormalcombinationIncidence:1in375newbornsTypesofstructurerearrangementsBalancedUnbalancedUnbalancedRearrangementsDeletion(del,缺失)Definition:isachromosomalmutationinwhichpartofachromosomeismissingIncidenceofautosomaldeletions:1/7000livebirthTypes:terminal(末端缺失),interstitial(中间缺失)（非平衡重排）Karyotype:46,XX,del(1)(q21)46,XX,del(1)(pter→q21:)TerminaldeletionLoss常见染色体结构畸变的描述方法：按国际规定的要求，依次先写明染色体总数，性染色体组成，然后用一个字母（如t）或三联字符号（如del）说明重排染色体类型的名称，其后在括号内写明有关的染色体号数，接着在另一括号内注明区、带号以表示断裂点。简式：只用其断点来表示：

46,XX,del(1)(q21)；繁式：在最后括弧内，描述染色体重排的带的组成：

46,XX,del(1)(pter→q21:)Karyotype:46,XX(XY),del(3)(q21q31)46,XX(XY),del(3)(pter→q21::q31→qter)

LossInterstitialdeletionReasons:Deletionsmayoriginatesimplybychromosomebreakageandlossoftheacentricsegment.Unequalcrossingoverbetweenmisalignedhomologouschromosomesorsisterchromatids.DeletionscanalsobegeneratedbyabnormalsegregationfromabalancedtranslocationorinversionDuplication(dup,重复)Definition:isachromosomalmutationthatresultsinthedoublingofasegmentofachromosome.正位重复反位重复Duplication(dup)Reasons:CanoriginatebyunequalcrossingoverByabnormalsegregationfrommeiosisinacarrierofatranslocationorinversion.RingChromosomes(r,环状)RingChromosome(r)Definition:deletionssometimesoccuratbothtipsofachromosome.Theremainingchromosomeendscanthenfuse,formingaringchromosome.ringchromosomelosslosslossIsochromosomes(I,等臂)Definition:isachromosomeinwhichonearmismissingandtheotherduplicatedinamirror-imagefashion.isochromosomereplicationafterreplicationafterreplicationisochromosomesIsochromosomes(i)Mechanisms:MisdivisionthroughthecentromereinmeiosisIIExchangeinvolvingonearmofachromosomeanditshomolog(orsisterchromatid)attheproximaledgeofthearm,adjacenttothecentromere.Isochromosomes(i)CommonIsochromosomes:i(Xq)i(18p)i(12p)DicentricChromosomes(dic,双着丝粒))Definition:adicentricisararetypeofabnormalchromosomeinwhichtwochromosomesegments(fromdifferentchromosomesorfromthetwochromatidsofasingleone),eachwithacentromere,fuseendtoend,withlossoftheiracentricfragments.dicentricchromosomeBalancedRearrangementsInversions(inv,倒位)Definition:occurswhenasinglechromosomeundergoestwobreaksandisreconstitutedwiththesegmentbetweenthebreaksinverted.Types:Paracentric(notincludingcentromere)Pericentric(includingcentromere)（平衡重排）ParacentricKaryotypes:46,XX,inv(1)(p22p34)46,XX,inv(1)(pter→p34::p22→p34::p22→qter)PericentricKaryotypes:46,XX,inv(2)(p15q21)46,XX,inv(2)(pter→p15::q21→p15::q21→qter)Inversioncarrier:acarrierofeithertypeofinversionisatriskofproducingabnormalgametesthatmayleadtounbalancedoffspringABACDBCDTheriskthatacarrierofaparacentricinversionwillhavealivebornchildwithanabnormalkaryotypeisverylowindeed.ABACDBCD臂间倒位携带者在形成生殖细胞的减数分裂过程中，根据在配子形成中同源染色体节段相互配对的规律，它将形成倒位圈，并且，经过在倒位圈内的交换，形成4种不同的配子，一种为正常染色体，一种为倒位染色体，另外两种均带有部分重复及部分缺失的重排染色体。这两种异常重排染色体各有一个着丝粒，属于稳定性畸变而可往后传递。因此其遗传效应主要决定于重复和缺失片段的长短及其所含基因的致死效应。一般来说，其倒位片段越短，则重复和缺失部分越长，形成配子和合子正常发育的可能性越小，临床表现为婚后不育、早期流产和死产的比例越高，娩出子女的可能性相对低；而倒位片段越长，则其重复和缺失部分越短，其配子和合子正常发育的可能性越大，娩出畸形胎儿的危险性相对较高Translocations(t,易位)Definition:involvestheexchangeofchromosomesegmentsbetweentwo,usuallynonhomologouschromosomesMaintypes:reciprocal(rcp,相互易位),Robertsonian(rob,罗伯逊易位)ReciprocalTranslocations(rcp)Definition:thistypeofrearrangementresultsfrombreakageofnonhomologouschromosomes,withreciprocalexchangeofthebroken-offsegments.Karyotypes:46,XX,t(2;5)(q21;q31)46,XX,t(2;5)(2pter→2q21::5q31→5qter;5pter→5q31::2q21→2qter)reciprocaltranslocationCarriersofbalancedreciprocaltranslocation:areassociatedwithahighriskofunbalancedgametesandabnormalprogenyFigure9-12.A,Diagramofabalancedtranslocationbetweenchromosome3andchromosome11,t(3;11)(q12;p15.5)平衡易位携带者在形成生殖细胞的减数分裂的前期I时，易位染色体将在联会时配对形成四射体。至后期I时，相关染色体可进行对位分离和邻位－1和邻位－2分离以及3:1分离。其中，仅有一种配子是正常的，一种是平衡易位的，其余都是不平衡的。与正常配子受精后所形成的合子中，大部都形成单体或部分单体、三体或部分三体患胎而导致流产、死胎或畸形儿。PairingatmeiosisSegregationUnbalancedUnbalancedNormalbalancedUnbalancedUnbalanced(50%)(50%)(rare)(inviable)(inviable)(viable)RobertsonianTranslocations(rob)Definition:thistypeofrearrangementinvolvestwoacrocentricchromosomesthatfusenearthecentromereregionwithlossoftheshortarms罗伯逊易位：又称着丝粒融合。在着丝粒部位或着丝粒附近部位发生断裂后，两者的长臂在两条近端着丝粒染色体着丝粒处结合在一起，形成一条由长臂构成的衍生染色体，两个短臂则构成一个小染色体，小染色体往往在第二次细胞分裂时丢失，这可能是由于缺乏着丝粒或其完全由异染色质构成所致。lossRobertsoniantranslocation14p1114p1121q1121q11Two(13q14q,14q21q)ofRobertsonia