醫(yī)學(xué)遺傳學(xué)教學(xué)課件：Chapter6 Genetic Variation in Individuals Mutation and Polymorphism

Chapter6

GeneticVariationinIndividuals:MutationandPolymorphismOutlineConceptsofmutationandpolymorphismCategoriesofHumanmutationsTheoriginofmutationsTypesofgenemutationsMutationNomenclatureHumangeneticdiversity---PolymorphisminDNATypesof

polymorphisminDNAMUTATION(突變)AnychangeinthenucleotidesequenceorarrangementofDNA

1.GenomeMutations（基因組突變）:mutationsthataffectthenumberofchromosomesinthecell2.ChromosomeMutations（染色體突變）:mutationsthatalterthestructureofindividualchromosomes3.GeneMutations（基因突變）:mutationsthatalterindividualgenesCategoriesofHumanmutations47,XY,+21

EtiologyofCriDuChatSyndromeTheOriginofMutationsGenomeMutations

missegregationofChromosomeduringmeiosisormitosis.SuchasDownsyndrome(seechapter9),cancercells

ChromosomeMutations

1/1700celldivisions，chrrearrangementGeneMutations1bp～10kbDNAreplicationerrorsMutationduringrepairofDNAdamage第一次減數(shù)分裂時21號染色體不分離

第二次減數(shù)分裂時21號染色體不分離減數(shù)分裂中染色體不分離有絲分裂中姐妹染色單體不分離

DNAreplicationerrorsStrictbase-pairingrulesandmolecularproofreadingreplicationerrors<10-10/bp/celldivision<1bp/celldivision

MutationduringrepairofDNAdamagespontaneouschemicalprocessoftenremainaspermanentmutationsGeneMutationsTypesofMutationandTheirEstimatedFrequenciesClassofMutationMechanismFrequencyExamplesGenomemutationchromosome10-2/celldivisionAneuploidy

missegregation

Chromosomechromosome610-4/celldivisionTranslocationmutationrearrangmentGenemutationbase-pairmutation10-10/basepair/celldivisionPointmutation10-5-10-6/locus/generationTypesofgenemutationsNucleotideSubstitutionsChainTerminationMutationsRNASplicingMutations“Hotspot”ofMutationsDeletionsandInsertionsDynamicmutations(動態(tài)突變)GENEMUTATIONNucleotideSubstitutionsMissensemutations(錯義突變):asinglenucleotidesubstitutioninaDNAsequencecanalterthecodeinatripletofbasesandcausethereplacementofoneaminoacidbyanotherinthegeneproduct.Accountforalmost50percentofalldisease-causingmutations(β-thalassemia)

3′···CTC···5′3′···CAC···5′mRNA5′···GAG···3′5′···GUG···3′polypeptidechain··Glu···Val·

phenotype

HbA

HbS

(Normal)

（thalassemia）

NormalMutantMissensemutationsDNA5′···GAG···3′5′···GTG···3′GENEMUTATIONNonsensemutations(無義突變):amutationthatgeneratesaterminationcondoncancauseprematurecessationoftranslation.Accountforapproximately12percentofalldisease-causingmutationsAhereozygousCtoTmutationconvertsargininecodon(CGA)toterminatecodon(TGA)GENEMUTATIONRNASplicingMutations1.Mutationsateitherthedonor(exon-intron)oraccepter(intron-exon)siteinterferewithnormalRNAsplicing.2.CreatealternativedonororacceptorsitesthatcompetewiththenormalsiteduringRNAprocessingAccountforapproximately10percentofalldisease-causingmutationsRNAsplicingGENEMUTATION“Hotspot”ofMutations

1.Transition:thesubstitutionofonepurinefortheother(AG)oronepyrimidinefortheother(TC).2.Transvertion:thereplacementofapurineforapyrimidine.MethylationofCintheCGdoubletgivesrisetoCTorGAtransition.Thus,theCGdoubletrepresentsature“hotspot”formutationinthehumangenome.Accountformorethan30percentofallsinglenucleotidemutation.

GENEMUTATIONDeletionsandInsertions

1.Smalldeletionsandinsertions

Frameshiftmutations(移碼突變):whenthenumberofbasesinvolvedisnotamultipleofthree,andwhenitoccursinacodingsequence,thereadingframeisalteredbeginningatthepointofthedeletionandinsertion.Smalldeletionsandinsertionsconstitutenearly?ofalldisease-causingmutations

2.Largedeletionsandinsertions

6%

ofalldisease-causingmutations(DMD,α-thalassemia)

3.DeletionsandDuplicationsCausedbyRecombination

Thepositionofamutationisdesignatedasbeingingenomic(i.e.,nuclear)DNA,cDNAsequence,mitochondrialDNA,orproteinbytheprefixg.,c.,m.,orp.,respectively.IncDNA,theAofthetranslationalstartATGisdesignated+1.Thenextbaseupstreamis-1;thereisno0

MutationNomenclature1.Anucleotidechange:thenucleotidenumberofthatbase,theoriginalnucleotide,agreaterthansymbol(>)andthenewnucleotideatthatposition.IngenomicDNA,thenucleotidesymbolsarecapitalized;InmRNA,theyarelowercase:c.1444g>a

Ifthefullgenomicsequenceisnotknown,thenucleotidesinanintron(“interveningsequence,”orIVS)arecountedas+1,+2,…+1istheinvariantGoftheGTinthe5’splicedonorsite,oras-1,-2,…countingbackfromthehighlyinvariantGoftheAG3’spliceacceptorsite:g.IVS33+2T>A,g.IVS33-2A>TMutationNomenclatureGU+1+2AG-2-12.Smalldeletions:thenumbersofthenucleotidesdeleted,separatedbyunderscore(___),followedbythetermdel,andthentheactualnucleotidesthathavebeendeleted.e.g.c.1524_1527delCGTA3.Smallinsertions:insafterthetwonucleotidesbetweenwhichtheinsertionoccurred,followedbytheactualnucleotidesinserted.e.gc.1277_1278insTATC

MutationNomenclature4.Amissenseornonsensemutation:attheleveloftheproteinbygivingthecorrectaminoacid,thepositionofthatresidue,andtheaminoacidthatreplacedthenormalone(Xforstopcodon):p.Glu6Val,p.Gln39XMutationNomenclatureHUMANGENETICDIVERSITYLocus(基因座)：

ParticularchromosomallocationAlleles（等位基因）：AlternativevariantsofgeneticsinformationataparticularlocusHaplotype(單體型)：Agroupofallelesincouplingatcloselylinkedloci,usuallyinheritedasaunit.Locus:A,B,CW,DW,DRAlleles:A1,A3,B5,B12,CW1,CW2…Haplotype:A,B,C,DHUMANGENETICDIVERSITYGeneticpolymorphism:Theallelesarefoundinmorethan1%ofchromosomesinthegeneralpopulation.

Rarevariants:<1%ofchromosomesofthegeneralpopulationInheritedVariationandPolymorphisminDNASinglenucleotidepolymorphisms(SNPs,單核苷酸多態(tài)性)Insertion-DeletionpolymorphismsMicrosatellitePolymorphisms（微衛(wèi)星多態(tài)性）MinisatellitePolymorphisms（小衛(wèi)星多態(tài)性）CopyNumberPolymorphisms（拷貝數(shù)多態(tài)性）Singlenucleotidepolymorphisms(SNPs)Morethan6millionSNPshavebeendiscoveredintheHumanGenomeProjectPolymorphismsthatresultfromvariationatasinglenucleotide.ComparewithmicrosatellitesandVNTRs.

MicrosatellitePolymorphismsMicrosatelliteMarkers

MicrosatellitearestretchesofDNAconsistingofrepeatingunitsoftwo,threeorfournucleotides,suchasTGTG…TG,CAACAA…CAA,orAAATAAAT…AAAT,oftenreferredtoasshorttandemrepeat(STR，短串聯(lián)重復(fù))polymorphisms.STRACACACPrimer1Primer2ACACACACACACACACACACACACACACACMicrosatellitemarkersinhumanDNADignosisMinisatellitePolymorphismsVNTR(variablenumberoftandemrepeat，可變數(shù)目串聯(lián)重復(fù))Polymorphisms

InsertionofmultiplecopiesofaDNAsequence10to100basepairsintheDNAbetweentworestrictionsite,knownasaminisatellite.CodominantinheritanceofaautosomalDNApolymorphismcausedbyVNTRCopynumberpolymorphismsConsistofvariationinthenumberofcopiesoflargersegmentsofgenome,rangingfrom200bptonearly2MbUsesofPolymorphismsinMedicalGeneticsMappingagenetoaparticularregionofachromosomebylinkageanalysisPrenataldiagnosesofgeneticdiseaseDetectionofheterozygouscarrierofgeneticdisease…ExamplesofInheritedVariationandPolymorphisminProteinsBloodGroupsandTheirPolymorphismTheABOSystemTheRhSystemTheMajorHistocompatibilityComplex(MHC)

Chapter8

GeneMappingDanwuOutlinePhysicalMappingMethods:SomaticcellhybridsGeneticMapping

Concepts:Linkage,LinkageAnalysis,Linkagedisequilibrium(LD)Methods:LinkageAnalysisGENEMAPPINGPhysicalMappingofHumanGenesGeneticMappingofHumanGenesbyLinkageAnalysis

Physicalmapping

AssigningagenetoaparticularbandofparticularchromosomeanditsrelationshiptoothergenesintermsofnumbersofbasepairsMethods:SomaticcellhybridsFISHGenomicSequencingSomaticcellhybrids

RandomlossofhumanchromosomesSomaticCellHybridsExtinction

IsolatecellsfromaffectedpatientMakecelllinesMakehybridsRetainhybridswiththediseasephenotypeIdentifychoromosomes

TheorderingofgenesonchromosomosaccordingtorecombinationfrequencyLinkageanalysisAssociationstudyStudieswithUnrelatedIndividualsFamily-baseddesignsforassociationstudiesGeneticMappingMappingHumanGenesbyLinkageAnalysisLinkageThetendencyforallelesclosetogetheronthesamechromosometobetransmittedtogether,asaintactunit,throughmeiosisGeneticLinkageAnalysis

Amethodofmappinggenesthatusesfamilystudies

todeterminewhethertwogenesshowlinkagewhenpassedonfromonegenerationtothenextLinkageRecombinationMeioticbehaviorofallelesattwolociareonthesamechromosomeThesmallertherecombinationfrequency,theclosertogethertwolociare.Therecombinationfrequency0-50%LinkageanalysisTrytolocalizegenesaffectingspecificphenotypesSearchfor:co-segregationofdiseaseandmarkerallelesUsespedigreedataGeneticMarkersSNP、STR、VNTRMarker-segmentofrecognizableDNAMarkerdoesnotnecessarilycodeforsomethingfunctionalEachchromosomehasseveralmarkeridentifiedCanstartassigningfunctionalgenestolocationsrelativetothemarkersSTRACACACPrimer1Primer2ACACACACACACACACACACACACACACAC132412345IIIIII1211221,22,53,42,32,31234122213431342213341FatherMotherChildMarkersandinheritanceSTR1STR2STR3Buildingblocksoflinkageanalysis

Chr.1Chr.22Chr.2121121211211521413212213451232421344714344232113222334GenotypesMarkermapsLikelihoodOdds(Lod)=

LikelihoodofdataiflociarelinkedataparticularθLikelihoodofdataiflociareunlinkedθ=0.50MaximumLikelihoodMethodLod

Scores(Z)

L(θ<0.5)Z=log10 L(θ=0.5)

Z3isconsidereddefinitiveevidencethattwolociarelinked(equivalenttogreaterthan1000:1oddsinfavoroflinkage)

Z1

suggestthatthetw