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Current trends in mapping human genes
Author: V. A. McKusick
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"Currenttrendsinmappinghumangenes 0892-6638/91/0005-0012/$01.50.� FASEB VICTORA.MCKUSICKJohnsHopkinsUniversitySchoolofMedicine,Baltimore,Maryland21205,USAABSTRACTThehumanisestimatedtohaveatleast50,000expressedgenes(geneloci).Someinformationis availableconcerningabout5000ofthesegenelociandabout1900havebeenmapped,i.e.,assignedtospecificchromosomes(andinmostinstancesparticularchromo-someregions).Progresshasbeenachievedbyacombina-tionofphysicalmapping(e.g.,studyofsomaticcellhybridsandchromosomalinsituhybridization)andgeneticmapping(e.g.,geneticlinkagestudies).New methodsforbothphysicalandgeneticmappingareex-pandingthearmamentarium.Theusefulnessofthemap-pinginformationisalreadyevident;thespin-offfromtheHumanGenomeProject(HGP)beginsimmediately.Thecompletenucleotidesequenceistheultimatemapofthehumangenome.Sequencing,althoughalreadyunderway forlimitedsegmentsofthegenome,willawaitfurtherprogressingenemapping,andinparticularcreationofcontigmapsforeachchromosome.Meanwhilethetech-nologyofsequencingandsequenceinformationhandlingwillbedeveloped.ItisarguedthattheHGPisanewformofcoordinated,interdisciplinaryscience;thatitsprimary objectivemustbeseenasthecreationofatoolforbio-medicalresearch-asourcebookthatwillbethebasisofstudyofvariationandfunctionforalongtime;thattheimpactonscientisttrainingwillbesalutarybyrelievinggraduatestudentsofuselessdrudgeryandbytrainingscientistscompetentinbothmoleculargeneticsandcom- putationalscience;andthatthefundingoftheHGPwillhaveaninsignificantnegativeeffectonsciencefundinggenerally,andindeedmayhaveabeneficialeffectthrougheconomyofscaleandafocusingofattentionontheex-citementofbiologyandmedicalscience. - McKusick,V.A.Currenttrendsinmappinghumangenes.FASEBJ..5:12-20;1991.KeyWords:chromosomepedigreepattern.familylinkage.genemapping.hybridization.genomics THEESSENCEOFMENDEL?SDISCOVERY(1865)isthatin-heritanceisparticulate.Thechromosomeswerefirstde-scribed12yearslaterbyWaltherFlemingofKiel.Meiosis,orthereductiondivision,asitwasthencalled,wasdescribedinthe1880s.Inpartasthebasisforrationalizingthereduc-tiondivisionofthechromosomesingametogenesis,the notionwasputforwardthatthechromosomescarryfactorsthatdeterminedevelopment:theRoux-deVries-Weissmannhypothesis.BeforetherediscoveryofMendelismin1900,E.B.Wilson,inthefirsteditionofhislandmarkmonographTheCellinDevelopmentandInheritance(1896),statedasfollows(pp.182-185): thechromosomeisacongeriesorcolonyofin-visibleself-propagatingvitalunits...,eachofwhichhasthepowerofdeterminingthedevelopmentofapar-ticularquality.Weismannconceivestheseunits ...[tobe]associatedinlineargroupstoformthe...chro-mosomes?? Thus,thechromosometheoryofheredityprecededtherediscoveryofMendelism.ThechromosometheoryofMen-delismwasadvancedbySuttonandBoveriin1902-1904.ThephenomenonoflinkagewasdiscoveredinthefirstdecadeofthiscenturyinthedomesticfowlbyBatesonandPunnett,whointroducedthetermscouplingandrepulsion. ThelineararrangementofMendel?sparticulateelementsofheredityalongthechromosomeandtheestimationofthein-tervalsseparatingtwosuchelements,bythencalledgenes(Johansson?sterm,about1909),weredevelopedbyThomasHuntMorganonthebasisofstudiesofDrosophilabeginningabout1911.UndergraduateAlfredH.Sturtevantwasimpor- tantindevelopingtheconceptoflinkagemapping.Alsoin1911,Morgan?scolleagueatColumbia,E.B.Wil-son,forthefirsttimeassignedaspecificgenetoaspecificchromosomeinamammal:thecolorblindnessgenetothehumanXchromosome.Hewroteasfollowsinhis1911paper(1): ?Inthecaseofcolor-blindness,forexample,allthefactsseemtofollowunderthisassumption[thatthegeneisontheXchromosome]ifthemalebedigametic(asGuyer?sobservationsshowtobethecaseinman).For,infertilizationthischaracterwillpasswiththeaffectedXchromosomefromthemaleintothefemale,and fromthefemaleintohalfheroffspringofbothsexes(Diagram,Fig.5).Color-blindness,beingare-cessivecharacter,shouldthereforeappearinneitherdaughtersnorgranddaughters,butinhalfthegrand-sons,asseemsactuallytobethecase? FriedrichHomer,aZurichophthalmologist,haddescribedthetypicalpedigreepatternofcolorblindnessin1876(2).AsHomerpointedout,thispedigreepatternwasknownalsoforhemophiliaandlateritwasrecognizedforafewotherdis-orders,whichbythesamereasoningasthatappliedbyWil-sontocolorblindness,mustalsobecodedbygenesonthehu- manXchromosome.Becauseofthedistinctivepedigreepattern,about36sex-linkedtraitsordisordersweredescribedinthehumanbeforethefirstX-linkedtraitwasdiscoveredinthemouse,about1950.Ontheotherhand,demonstrationofautosomallink-agesproceededmuchfasterinthemousebecauseexperi- mentalmatingssuchasthehighlyinformativedoubleback-crossmatingcouldbedoneexperimentallyinthatspecies.Thefirstlinkageinamammalwasthatdemonstratedbe-tweenalbinismandpinkeyein1915byJ.B.S.HaldaneandhissisterNaomi,workingwithA.D.Sprunt(3).Theauthorsgavethefollowingexcuseforpublishingaprelimi- naryreport:?Abbreviations:RFLP,restrictionfragmentlengthpolymor-phism;VNTR,variablelengthtandemrepeats;PlC,polymor-phisminformationcontent;PCR,polymerasechainreaction;YAC,yeastartificialchromosome;HGM,humangenemapping;GDB, genomedatabase;CEPH,Centred?EtudesduPolymorphismeHumain. 1500 1000 500 #{149}I#{149}IX-chromosomal 66687072747678808284868890Year MAPPINGHUMANGENES 13 ?Owingtothewarithasbeennecessarytopublishprematurely,asunfortunatelyoneofus(A.D.S.)hasalreadybeenkilledinFrance??AlthoughtheintervalseparatingthehemophiliaandcolorblindnesslociontheXchromosomewasestimatedbyHaldaneandcolleagues intwoseparateanalysesin1937and1947,noautosomallinkagewasdemonstrated,letalonequantitated,until1951-aboutthesametimethatthefirstX-linkedtraitwasdemonstratedinthemouse.JanMohr,inhisdoctoralthesisinCopenhagen,foundlinkageofLutheranbloodgroupwithsecretorfactor.Hisstudiesalsosuggested linkageofthesetwolocitothatformyotonicdystrophy,afindingthatwassubsequentlyconfirmed.Indeed,thethreelociwereshowntobeonchromosome19,anditwasmainlyworkinthedepartmentofProfessorJanMohr,bythenthelong-timedirectoroftheInstituteofMedicalGeneticsatCopenhagen,thatprovidedthecriticalevidenceofthechro- mosomallocationofthislinkagegroup.Inhisstudiesintheearly1950s,JanMohrmadeuseofthesib-pairmethodofPenrosebasedontheprinciplethatiftwolociarelinked,sibswillfailtoshowrandomassociationoftraitsdeterminedbygenesatthoseloci.Themethodofes-timatingthelikelihoodoflinkageaccountingforfindingsin particularpedigreeswasdevelopedbyworkerssuchasC.A.B.SmithandNewtonMortoninthe1940sand1950s.Thisworkwasthebasisofthenowfamiliarlodscore-thelogarithmoftheoddsoflinkageasopposedtononlinkage(4).Between1951and1968,whichisthenextwatershedyear, anumberoffurtherautosomallinkagesweredescribed,suchasABOvs.nail-patellasyndromeandRhvs.elliptocytosis-1.Butforalltheseautosomallinkages,theprecisechromosomecarryingthegeneswasnotknown.In1968,RogerDonahue(5),thenacandidateforaPh.D.degreeinhumangeneticsatJohnsHopkinsUniversity,demonstratedinhisownfami- lylinkageoftheDuffybloodgrouplocustochromosomeIasdistinctivelymarkedinhimandanumberofhisrelativesbyaso-calledheteromorphism.Therelativelyeasystudyofhumanchromosomesandtheintroductionofcytogeneticstotheclinichadcomeintheprevious10years.Donahue?sun-usualchromosomeinpreparationsmadein1968inthejust prebandingerahadtheappearanceofanuncoiledareasub-jacenttothecentromere.(Withtheadventofbandingmethodsabout1970,especiallycentromericbanding,itwasclearthattheanomalyrepresentedanunusuallylonghetero-chromaticsegment.)Donahuerealizedthatthismightbesegregatingasadominanttrait,asitwasdemonstratedby oneofthetwochromosomes1,andcouldthereforebeusedasalinkagemarker.Furthermore,hehadthegumptiontodoalinkagestudy,whichwasnoteasybecauseofhisfar-flungfamilyforcollectingbloodsamplesandbecauseofthelaborinvolvedinthetestingofmarkers.IntheDonahuepedigree,thelodscoreforlinkageof Duffybloodgrouptothelongheterochromaticsegmentofchromosome1wasfarbelowthefigureof3.0(1000to1oddsonlinkage)generallytakenasevidenceforlinkagenowa-days.However,theobservationwasquicklyconfirmedbyothers.Manystudiesoflinkageoflocionchromosome1,wherenowmorethan190geneshavebeenlocated(seelater), indicatethattheDuffybloodgroupisontheproximalshortarm,i.e.,ontheoppositesideofthecentromerefromthelongheterochromaticsegmentwithwhichitshowslinkage.Theremaybesuppressionofcrossing-overinthepericentricregionfavoringdemonstrationofthelinkage. By1968,whenthefirstautosomalassignmentwasmade,about68geneshadbeenassignedtotheXchromosomeonthebasisofcharacteristicpedigreepatterns.(Theregionallocationofthe68ontheXchromosomewasknownfornoneofthem.)Thegrowthofinformationonchromosomalas-signmentsisdiagramedinFig.1.AsofSeptember10,1990, 1868expressedgeneshadbeenassignedtospecificchromo-somes(Table1),andinmostinstancestospecificbandsofthosechromosomes.Thishasbeenpossiblebecauseoffourcomminglingmethodologicstreams:1)familylinkagestudy,2)chromosomestudy,3)somaticcellgeneticstudy,and4)moleculargeneticstudy(Fig.2). Beginningabout1970,mappingtookoffatanacceleratedpace,particularlythroughtheuseofsomaticcellhybridiza-tion.Thesortingoutofthechromosomesinthesubclonesderivedfromrodent-humanhybridcellswascomparabletotheassortmentofhumanchromosomesinmeiosis.SomaticcellhybridizationwasthuswhatPontecorvoreferredtoasa parasexualmethodandwhatHaldanecalledasubstituteforsex.Thedevelopmentofchromosomebanding,alsoabout1970,providedahighlyimportant,indeedessential,methodologicelementbypermittingtheuniqueidentifica-tionofeachhumanchromosomeandthedifferentiationofhumanchromosomesfromrodentchromosomesinthe hybridcells.About1980,afurtheraccelerationingenemappingoc-curredwiththeintroductionofmoleculargenetictech-niques.RecombinantDNAtechnologyprovidedprobesthatcouldbeusedinthreeways:first,inconnectionwithDNAsfromsomatichybridcells(obviatingthenecessitytohave geneexpressionintheculturedcells,asonecoulddirectly?goforthegene?);second,forinsituhybridizationtochro-mosomespreads;andthird,asDNAmarkers-e.g.,restric-tionfragmentlengthpolymorphisms(RFLP5)andvariablelengthtandemrepeats(VNTRs) -infamilylinkagestudies(6).Chromosomessortedbymeansofthefluorescence-activatedcellsortercouldalsobeprobedwiththenewar-mamentarium.(Chromosomesortingbythisphysicalmethodservesthesameroleasmeiosisinvivoandsomaticcellhybridclonesinvitro.Insituhybridizationandsomaticcell hybridizationaremethodsofphysicalmapping;familylink- aI Figure1.Growthofinformationonchromosomeassignments. FLS ciiDoosga11(001(0)(qooolouone(Eoch.woenoppnS(EM)on,(on,e.g.deiwion(cb)Vinn.iothwodcl,oegw(F) AOoigno.eo,bySCH(S)Rogoeolmo#{231}p,ogbySCH(S)g000lo*oufw.CMGT(C) (A)Molecoluean&yoo01flow00,104cIo,ono.000000(REb) SSCMuyoiooytool(S)Rdtoankgoowoefltogwcoo(R)goonvender.MCOT(M) DN00RItAhybnd.tattooIn1010400US)Sombem100lyws(REdDNA.n,etbotedgotUOnSIw,DMGT(DM) Rothcuon000ymulinetapping(RE)DNAnoqoendng(NA)M- (AAS)Figure2.Fourcomminglingmethodologicstreams. TABLE1.Numberofgeneassignmentsbychromosome0 14Vol.5January1991 TheFASEBJournal McKUSICK ChromosomeNo.ofgenesChromosomeNo.ofgenes1 19413 242 11014 603 68 15 514 74 16 68 5 72 17 1076 10418 237 10719 918 53 20 349 59 21 3610 58 22 58 11 132X 18712 100Total1868#{176}Numberofexpressedgenesassignedtoeachchromosome(HumanGeneMappingWorkshop10.5,Oxford,England,September10,1990). agestudiesgiveinformationonthegeneticmap,butwhenthemarkersusedhavebeenmappedtospecificchromosomalsites,physicallocationcanbeinferred.)STATUSOFTHEHUMANGENEMAPASOF SEPTEMBER10,1990AttheHumanGeneMappingWorkshopinOxfordearlyinSeptember,1990,theavailableinformationonthehumangenemapwascollated,withresultsthataretabulatedinTableIandFig.3.Atotalofalmost1900geneshavebeen mappedtospecificchromosomallocations.Inaddition,morethan4500DNAsegments,so-calledanonymousDNAsegmentsbecausetheirfunction,ifany,isnotknown(indeedmostareknownnottobeexpressed),havebeenmappedtospecificchromosomalsites.Abouthalfofthesesegmentshavebeenshowntobepolymorphicandmanyofthemare sufficientlyvariabletomakethemusefulaslinkagemarkers.Thehumanisestimatedtohaveabout50,000genes,almostcertainlynotmorethan100,000.Onthebasisofin-directarguments,estimatesofthisorderwerearrivedatinthepast;inmorerecenttimes,studiesofthedensityofgenesonthechromosomesandinformationontherangeofsizes ofgenessupporttheseestimates.Manymoregeneshavebeenassignedtosomechromo-somesthantoothers,ifoneexamineseithertheabsolute(Fig.3A)ortherelativenumbers,derivedbydividingtheab-solutenumberbythelengthofthechromosomeexpressedasapercentageofthelengthofthehaploidsetofautosomes (Fig.3B).ThepreponderanceoflociontheXchromosomederivesfromtherelativeeaseofassignmentbypedigreepat-tern;thisfactorwasaidedbytheavailabilityofaselectionsystem,basedontheX-linkedHPRTlocus,thatcouldbeusedinmappingbysomaticcellhybridization.Thelargenumberonchromosome17isrelatedinlargeparttothe availabilityoftheselectionsystembasedonthethymidinekinaselocusonthatchromosome.Chromosomes11and16areratherwellmapped,perhapsparticularlybecauseofthelocationthereofthe/3-globinanda-globinloci,respectively.Chromosome16alsohadagoodlinkagemarkerearlyonintheformofthehaptoglobinlocus.Chromosome6hadthe advantageofHLA,asuperbhighlypolymorphicmarkersys-temforgeneticlinkage.Chromosome7underwentintensivestudywhenitwasdiscoveredthatthecysticfibrosislocusmapsto7q.Chromosome21hashadattentionfortheobvi-ousreasonofinterestinDownsyndrome.Thestrongperfor- manceofchromosome22mayberelatedtothefactthattheXlight-chaingenesarethere,andtheBCR/ABLfusiongenethatresultsfromthe9;22translocationofchronicmyeloidleukemiahasstimulatedmuchstudy.Thereasonforthelargenumberofgenesassignedtochro-mosome19(thehighestrelativenumbersecondonlytothe X)maybemerelythatitgotstartedearlywiththesecretor!Lutheran/myotonicdystrophylinkagegroup,andtherela-tivelylargenumberonchromosome1mayhavethesameex-planation.Isitpossiblethatsomechromosomesaregenicallylessdenselypopulatedthanothers?Chromosomes13and18standoutforalownumberofmappedgenes.Itisnote- worthythatexceptforthesmallestautosome,no.21,onlynos.13and18showtrisomythatiscompatiblewithlivebirth.Thisfactsuggestsalsothattherearerelativelyfewgenesoratleastfewgenesofcriticalimportanceonthesechrorhosomes.Inparallelwiththemappinginhumans,genemapping hasbeenproceedingapaceinthemouse,whichisthemostusefulmammaliangeneticmodelforthehumanbecauseoftheextensiveamountofgeneticinformationavailable,andtherelativeeaseofexperimentalmanipulation.Atthesametime(June,1976),mappinginbothmouseandthehumanachievedthepointthatatleastonegenehadbeenassigned toeverychromosome.Althoughinthemouse,asmentionedearlier,linkagemappingproceededmuchfasteruntilthesurrogatemethodssuchassomaticcellhybridizationweredeveloped,thehumanhasoutpacedthemouseinrecenttimes.Caenorhabditiselegans,anematode,isalsoausefulmodel (7).Asinhumans,thereisextensiveanatomicandphysio-logicinformation,andrelativelyspeaking,thegeneticanddevelopmentalinformationisevenmoreextensivethaninhumans.Thedevelopmentallineageofeachofthe959cellsoftheorganismisknown;allthesynapsesofthenervoussys-temaredescribed;andmorethan1000geneshavebeen HUMANGENEMAPPINGFOURCOMMINGLINGMETHODOLOGICSTREAMSFamIySiodiochromosomeStudiosSomaticCellStudiosMolecularStudios Lthbg,(F)U.wbugodtheqmlthnoo.Unkugawithheoso.owuyi,ianw.,m,geoos*)(Ho,soiogyCtsymosy.H)LiwkgawithRPLP,(Pd)LD)(QoonsoOmon.OT)Deithoomapog(N) (qwJ(Iouve) 12345678910111213141516171819202122XA Chromosome 12345878910111213141516171819202122XChromosome 7thed.6thed. 4thed.3rded. 1990 MAPPINGHUMANGENES 15 Angeles(R.Sparkes,organizer),Helsinki(A.delaChapelle,organizer),Paris(J.Fr#{233}zal,organizer),andagainNewHaven(F.RuddleandK.Kidd,co-organizers).Thework-shopinearlySeptember,1990,washeldinOxford,England,underthedirectionofSirWalterBodmerandIanCraig.FortheseHGMworkshopsacommitteewithco-chairsassumed responsibilityforcollatingtheinformationonthegenemapofeachchromosome.AstandingcommitteeoftheHGMworkshops,cochairedbyPhyllisJ.McAlpineandThomasB.Shows,rendersopinionsonmattersofnomenclature,partic-ularlychoiceofgenesymbols,toassureconsistency.Com-mitteesattheworkshopsareresponsibleforotheroverall considerations,namely,acommitteeonclinicaldisordersthathavebeenmapped,andacommitteeonneoplasiathatreportsonspecificchromosomalchangesassociatedwithspecificneoplasms,aswellasthemappingofoncogenesandgenesatclonedbreakpointsinthechromosomerearrange-mentsinneoplasia,andrecently,lossofheterozygosityand coamplificationofgenesinneoplasmsasindicatorsofmaplocation.BeginningwiththemostrecentOxfordworkshop,thedataonthehumangenemapareentereddirectlyintoadatabasethatwillbecontinuouslyupdated.Thisdatabase,maintainedinBaltimoreatJohnsHopkinsUniversitywith thesupportoftheHowardHughesMedicalInstitute,iscalledGDB(forgenomedatabase).Thechairsofeachofthecommitteeswillberesponsibleforongoingediting,whichtheycanperformfromremotesites.Furthermore,thedata-basewillbegenerallyaccessiblebythescientificcommunityworldwide.ItsdevelopmentisunderthedirectionofDr. PeterPearson,formerlychairmanoftheDepartmentofHumanGeneticsinLeidenUniversity,andaleadingcytogeneticistandgenemapper.Thedevelopmentofthesys-temsunderlyingGDBhasbeentheresponsibilityofRichardLucier.FullyintegratedwithGDBanddistributedworldwide alongwithit(andindeedamainreasonforthedevelopmentofGDBinBaltimore)isOMIM,theon-lineversionofMen-delianInheritanceinMan(8),theencyclopediccatalogofgenesthatIhavemaintainedoncomputersincelate1963andhavepublishedasacomputer-basedbooksince1966(9thedition,1990).MycolleaguesandIhaveprovidedthescientificand medicalcommunityaccesstotheon-lineversionformorethan3years.AlthoughtheprintversionhasappearedatB TotalNumberofEntriesinMendellanInheritanceInManFigure3.A)Numberofgeneassignmentsbychromosome.5077 l5Sspt.1990B)Relativedensityofgenesassignedtoeachchromosome(see5000text). 9thed.mappedtooneoranotherofthefourchromosomepairs. ed.Contigmapsareapproachingcompletion.Nowwhatre- mainsisnucleotidesequencing.UITHESOCIOLOGYOFHUMANGENEMAPPINGInformationonthehumangenemaphasbeencollatedinaseriesofhumangenemapping(HGM)workshops.Thefirst 2000ofthesewasconvenedatYalebyFrankRuddlein1973,withthefinancialsupportofTheMarchofDimes,representedbyDr.DanielBergsma,VicePresidentforProfessionalEduca-0lion.SubsequentworkshopswereheldinTheNetherlands 196019701980(D.Bootsma,organizer),Baltimore(V.A.McKusick,or-ganizer),Winnipeg(J.Hamerton,organizer),EdinburghYear(J.Evans,organizer),Oslo(K.Berg,organizer),LosFigure4.GrowthofentriesinMIM. 16Vol.5January1991 TheFASEBJournal McKUSICK 2-yearintervals,inrecenttimestherapidevolutionofthefieldgivestheon-lineversiontheextravalueoftimeliness.Anotheradvantageoftheon-lineversionistheabilitytosearchthedatabaseelectronically.Thesizeofthedatabaseisreflectedbythenumberofentries,morethan5,000(Fig.4),eachrepresentingasinglegenelocus,aswellasby thecountsofindividualauthors(morethan56,000)andreferences(morethan36,000).Thedatabaseisclearlytoolargetobehandledefficientlybyprintindices.WithintheUnitedStates,OMIMand(morerecently)GDBhavebeeneasilyaccessiblethroughTelenetandInter-net;accessandeventranscriptionchargeshavebeenwaived throughthegenerosityoftheHowardHughesMedicalInsti-tute.2Tofacilitatedistributionelsewhereintheworld,ar-rangementshavebeenmadefordistributionnodesintheUnitedKingdom,Germany,Sweden,andJapan.Figure4indicatesthegrowthinnumberofentriesinMIMoverthe25yearsofitsexistence.Theprincipleisthat nomorethanoneentrypergenelocusiscreated.Alltheal-lelicmutationsatagivenlocusarelistedunderasingleentry.Thus,thetotalgivessomeindicationoftheproportionofallgenesaboutwhichwehaveinformation.Thatpropor-tionisnowabout10%.Untilabout1980,theonlymethodforidentifyinggeneswastheoccurrenceofMendelianvaria- tion;hencethetitle,MendelianInheritanceinMan.Inrecenttimes,ofcourse,geneshavebeencloned,mapped,andse-quencedwithoutanyMendelianvariationinphenotypehavingbeenassociatedwiththem.Suchgeneshavede-servedlybeenincorporatedasentriesinMIM.Thesehavecontributedgreatlytotherecentlyacceleratedpaceofacces- sions.METHODSOFMAPPING,OLDANDNEWAsindicatedbyTable2,somaticcellhybridizationinallits variationshasbeenbyfarthemostproductivemethodofhumangenemapping.Themethodsecondinpositionisinsituhybridizationwhichattainedthisplacebythefallof1987.Itsrapidascendancyisinsomewayssurprisingbe-causethemethodwasmadetoworkreliablyforsingle-copygenesonlyasrecentlyas1981.Presently,wheneverageneis cloned,onehasnotadequatelycharacterizedituntilonehasmappedit,first,bydeterminingitschromosomallocationbyhybridizingageneprobetoapanelofDNAsfromsomaticcellhybrids,andsecond,bycorroboratingthatassignmentandregionalizingitbyinsituhybridization.IfanewlyclonedgeneisfoundtohaveanassociatedRFLP,thereisa TABLE2.MethodofmappingMethod No.oflocimappedSomaticcellhybridization1148 Insituhybridization687Familylinkagestudy 466Dosageeffect 159Restrictionenzymefineanalysis176Chromosomeaberrations123Homologyofsynteny 110 Radiationinducedgenesegregation18Others 143Total 3047#{176}Numberofautosomallocimappedbyseveralmethods,September15,1990. thirdmethodformappingthegene:linkageagainstDNAmarkersthathavepreviouslybeenmappedintheCentred?EtudesduPolymorphismeHumain(CEPH)families.TheCEPHinParis,developedbyNobelLaureateJeanDausset,hasacollectionofcelllinesfrommorethan40three-generationfamiliesinwhichallfourgrandparentsandeight ormoregrandchildren,aswellastheirparents,havebeenavailableforsamplecollection.TheDNAsfromthefamilieshavebeensubjectedtolinkagestudiestocreateareferencemapforeachchromosome.Nonisotopiclabelingforinsituhybridization(9,10)hastheadvantagethatonedoesnotneedtowaitfordevelopmentoftheautoradiographsorhave thenuisanceandexpenseinvolvedinthehandlingofradio-isotopes.Inaddition,onecanexpecttostudytherelativepo-sitionoftwoormoregenesbyusingfluorescentmarkersofdifferentcolors.Thereare,however,manygenes,includingclinicallyim-portantdisorderssuchascysticfibrosis,Huntingtondisease, andpolycystickidneydisease,thatcouldnotbemappedbyfirstcloningthegenebecausethenatureofthemutantgeneproductwasnotknown.Inthesecases,mappingofthephenotypebyfamilylinkagestudieshasbeennecessary.TheavailabilityofDNAmarkerssuchasRFLPs,distributedmoreorlessuniformlyoverthegenomeatintervalsof5to 10centimorgans(cM)toconstitutealinkagereferencemap,meansthatthechancesaregoodthatlinkagecanbedemon-stratedbetweenagivenraredominant(orevenrecessive)andoneofthemarkers.TheinformativityofaparticularRFLPdependsonitsdegreeofheterozygosity.Onthesug-gestionofBotsteinetal.(6),theinformativityismeasured bythePlC(polymorphisminformationcontent)value.PlCisthesumoftheproportionofallparentalmatingsthathaveatleastoneheterozygousparent.ThedisorderslistedinTable3wereallmappedbygeneticlinkagetomarkers.Theapplicationofthepolymerasechainreaction(PCR)tosinglesperm,inthehandsofArnheimandhiscolleagues (11,12),permitsthedirectascertainmentoflinkageandesti-mationofrecombinationfrequencies.Itislikedeterminingdirectlythegeneticcompositionofthestickdiagramsusedintextbookstoexplainlinkageandrecombinationandpre-sentingthedataderivedfromfamilystudies.Themethodhasthepotentialadvantagethatonecanstudylargenum- bersofmeiosesfromasingledoublyheterozygousmale.Or-dinarily,inhumanfamilies,whenonemustdependonanal-ysisofthephenotypeofhisoffspringforidentificationofrecombination,onehasanopportunitytostudynomorethan8or10,orintrulyexceptionalcircumstances,16or18meiosesfromasinglemale.Becauseofthelargenumberof meiosesthatcanbestudiedbytheArnheimmethod,infor-mationoncloselinkagecanbedetermined.Furthermore,thepossibilityofdifferencesinthefrequencyofrecombina-lioninthesameDNAsegmentindifferentmalescanbestudied,aswellastheeffectofageintheindividualmale.Linkagedisequilibriumcanbeusedasacluetocloselink- age.Inasense,homozygositymappingofrecessivegenes(13)isbasedonthisprinciple.InapopulationsuchastheAmishortheFinnswherefoundereffectmakesitlikelythatallcasesofagiven,ordinarilyrarerecessivearedescendentsfromacommonancestor,oneexpectsthatgenescloselysitu-atedtothedisease-producingallelewillstandagoodchance ofbeingtransmittedtoaffecteddescendantsandnottothe2Forestablishingaccess,contactGDB/OMIMUserSupport,WelchMedicalLibrary,JohnsHopkinsUniversity,1830E.Monu-mentSt.,Baltimore,MD21205,USA.Tel.:(301)955-7058;FAX: (301)955-0054. lipilq1lq13q13qI5qI6p 16pIfiq17q9q19q21q22q XpXpXqofmappedMendeliandisordersforwhichthebiochemicalbasiswasnotpreviouslyknown(mappingasafirststeptowardbasicunder- standing). tidesrepresentedbytherecognitionsitefortherestrictionenzyme,therareristhecutsiteandthelargerthefragmentsthatareproduced.Inaddition,themethodsforseparatinglargefragments,ofwhichtheSchwartzandCantormethodofpulsedfieldgelelectrophoresiswasapioneer,providethematerialthatcanbeusedforhybridizationofgeneprobes. GiventhatgeneAhasbeenassignedtoaparticularlocationinthegenomebysomeothermethod,ifgeneBhybridizestothesamelargefragment,onehasdeterminedwheregeneBislocatedalso,aswellasplacedanupperlimitontheinter-valseparatinggenesAandB.Restrictionmappingusingfre-quentlycuttingendonucleasescandefinetherelationshipof AandBinmoredetail.Yeastartificialchromosome(YAC)cloningalsoprovideslargeDNAfragmentstowhichclonedgenescanbehybridizedformappingpurposes.THEROLEOFGENEMAPPINGINHUMAN BIOLOGYANDMEDICINEAsSirWalterBodmerhaspointedout,whatseemedlikearatherreconditeactivitywhenthehumangenemappingworkshopswereinitiatedin1973hasachievedacentralroleinbothhumanbiologyandscientificmedicine.Charles ScriverofMontrealsuggestedthatgenemappingisprovid-inganeo-Vesalianbasisformedicine.Beginninginthe1950s,theavailabilityofrelativelyeasymethodsformicroscopicstudyofthehumanchromosomesgavetheclini-calgeneticist?hisorgan?andabettedthedevelopmentofhu-mangeneticsasaclinicalspeciality.Continuallyimproving methodsofchromosomestudy,andparticularlythemethodsformappinggenesonchromosomes,havegivenallofmedi-cineanewparadigm.Specialistsinallmedicalareasap-proachthestudyoftheirmostpuzzlingdiseasesbyfirstmap-pingthegenesresponsibleforthem.Thus,justasVesalius?sanatomicaltextof1543formedthebasisforthephysiology ofWilliamHarvey(1628)andthemorbidanatomyofMor-gagni(1761),genemappingishavingawidelypervasiveinfluenceonmedicine.Inexaminingthesignificanceofmappinginformationinclinicalmedicine,itmaybeusefultosubstitutetheanatomi-calmetaphor(theanatomyofthehumangenome)forthe cartographicmetaphor(thehumangenemap).Theana-tomicmetaphorpromptsonetothinkintermsofthemorbidanatomy,comparativeanatomyandevolution,functionalanatomy,developmentalanatomy,andappliedanatomyofthehumangenome.Theapproximately1900expressedgenesthathavebeen mappedtospecificchromosomes,andinmostinstancestospecificchromosomeregionsorbands(Table1),codeforbloodgroups,enzymes,hormones,clottingfactors,growthfactors,receptors(e.g.,forhormonesandgrowthfactors),cytokines,oncogenes,structuralproteins(e.g.,collagensandelastin),etc.Theyalsocodeforalargenumberofdisease genesforwhichthebiochemicalbasisisnotknownorwasnotknownbeforethemapping(Table3).Inall,thechromosomallocationofover500geneticdis-orders(themorbidanatomyofthehumangenome)hasbeen 3Haplotypereferstothecombinationofspecificallelesatseveralcloselylinkedloci,e.g.,thehaplotypesatthemajorhistocompatibil-itycomplexforHLAtypes,suchasA3,B27,C2,DR2.Theap-proachwasadaptedtotracinga-thalassemiasandsicklecellanemiaintheearly1980sandmorerecentlyhasbeenusedinthestudyofinbornerrorsofmetabolismsuchasPKUandcysticfibrosis. unaffected.Thecloserthegenesthegreaterthechancethatboththemarkerandthediseaseallelewillremainonthesamechromosomeinmostaffectedpersons.Thisistheargu-mentunderlyingtheuseofhaplotypes3toidentifythepresenceofthalassemiaorotherdiseasegenes.IntheAmish,becauseofthedefinedgenealogies,DNApanelsthatreflect anidentifiablenumberofmeiosesmightbeusedinthesamewaythereferencefamiliesinCEPHareused.(Homozygositymappingbearssimilaritiesinprincipletomappinginmicebyuseofrecombinantinbredstrains)(14).GossandHarrisinthe1970sdevelopedamethodforde-terminingtheintervalbetweengenesonthebasisofthe chancethattheywouldbeseparatedwhenastandarddoseofradiationwasadministeredtothecell.Theradiatedcellwasrescuedbyhybridizationwitharodentcell.Thismethodofradiation-inducedgenesegregationorradiationmappinghasbeendevelopedrecentlybyDavidCoxandothers(16,17).Theproductmightbecalledthe?zapmap,?atermCox doesnotlike.InrecenttimeswehavelearnedhowtouseenzymesthatcuttheDNAonlyrarely,atintervalsofafewhundredkilo-basesormore.Ingeneral,thelargerthenumberofnucleo- TABLE3.DiseasesmappedbyRFLPs#{176} MAPPINGHUMANGENES 17 Charcot-Marie-Toothdisease1q,17,Xq13UshersyndromelqvanderWoudelip-pitsyndromelqAniridia 2p,lipWaardenburgsyndrome2qvonHippel-Lindausyndrome3pHuntingtondisease4p Facioscapulohumeralmusculardystrophy4qSpinalmuscularatrophy,severaltypesSqAdenomatouspolyposisofcolonHemochromatosisJuvenilemyoclonicepilepsy6pSpinocerebellarataxia(oneform)Craniosynostosis Greigcraniopolysyndactylysyndrome7pCysticfibrosis7qLanger-Giedionsyndrome8qFriedreichataxia 9qTorsiondystonia9qTuberoussclerosis9q,1lqNail-patellasyndrome9q Multipleendocrineneoplasia,typeII lOqWilmstumor-iMultipleendocrineneoplasia,typeIAtaxia-telangiectasiaRetinoblastomaWilsondiseaseMarfansyndrome PolycystickidneydiseaseBattendiseaseCataract,MarnertypeNeurofibromatosisMyotonicdystrophyMalignanthyperthermia Alzheimerdisease(oneform)Acousticneuroma,bilateralDuchennemusculardystrophyRetinitispigmentosa(twoforms)Wiskott-AldrichsyndromeAlportsyndrome Diagnosis(prenatal.preclinical,Carrier)bythelinkagepnncipleDeterminationofGenDetectbycandidategeneapproachorbyreversegenetics specificDNADiagnosis(prenatal.preclinical.carrier)SouthernanalystsASO(allele.specificoligonucleotide)analysisPCR(polymerasechainreaction)amplificationandsequencing Etc. Improvedmanagementfrombetterunderstandingofpathogenesls Figure5.Clinicalapplicationofgenemapping.18Vol.5January1991 TheFASEBJournal McKUSICK determined.Forsomedisorders,themappinghasbeendonebylocatingthewild-typegenesuchasthatforphenylalaninehydroxylasewhichisdeficientinphenylketonuria(PKU)andmapsto12q.Inotherdisorders,themendelizingclinicalphenotypehasbeenmappedbyfamilylinkagestudiesusinganchormarkerssuchasRFLPs;examplesareHuntington disease,polycystickidneydisease,andMarfansyndrome.Inyetotherdisorders,mappinghasbeendonebybothap-proaches;forexample,elliptocytosis,typeI,wasmappedtothedistalregionoftheshortarmofchromosomeIbylinkagetoRhandothermarkerssituatedthereandalsobymappingofthegeneforprotein4.1(whichismutantinthatdisorder) tothesameregion.Todate,theappliedanatomyofthehumangenomehasrelatedparticularlytothosedisordersforwhichthebasicbiochemicaldefectwasnotyetknown(Fig.5).Becauseofthisignorance,itimpossibletodeviseafullyspecificdi-agnostictestortodesignrationaltherapy.Oncethechro- mosomallocationofadisease-producinggeneisknown,togetherwithitsproximitytoothergenesandespeciallyDNAmarkers,onecandodiagnosis(prenatal,presympto-matic,andcarrier)bythelinkageprinciple.Furthermore,onecanexpecttodeterminethefundamentalnatureofthegeneticlesionbywalkingorjumpinginonthegene,a processoftenlabeled,withquestionableappropriateness,reversegenetics.Then,knowingthenatureofthewild-typegene,onecanworkoutthepathogeneticstepsthatconnectgenetophene,mutationtoclinicaldisorder.Secondarypreventionandtherapythroughmodificationofthosestepscanbedeveloped.Inmanyinstancesgenetherapywillprob- ablyfindgenemappinginformationusefulbackground.Inconnectionwiththemorbidanatomyofthehumangenome,mapping,morethananyothersinglefactorperhaps,hasbeenresponsibleforestablishingthechromo-somebasisofcancer:bythedemonstrationofspecific,microscopicallyevidentchromosomalaberrationsinassocia- tionwithspecificneoplasia,bythemappingofoncogenesandantioncogenes(recessivetumorsuppressorgenes),andbycorrelationofthetwosetsofobservations.Somaticcellgeneticdiseaseasthebasisnotonlyofallneoplasiabutalsoofsomecongenitalmalformationsandprobablyofautoim-munediseasesjoinsthethreecardinalcategoriesofdisease astogeneticfactors:singlegenedisorders,multifactorialdis-orders,andchromosomaldisorders.Mitochondrialgeneticdiseaseisafifthcategory.Themitochondrialchromosome,the25thchromosome,wascompletelysequencedby1981inthelaboratoryofFredSangeratCambridge,anditsgenesweremappedinthe6 (locationofgenestospecificchicimosomesitesandloridentificationoftheirnearneighbors) yearsthatfollowed.DeletionsandpointmutationsinthemitochondrialchromosomewerethenidentifiedasthebasisofLeberopticatrophy,myotonicepilepsy/raggedredfiberdisease,Pearsonpancreas-bonemarrowsyndrome,oncocy-tomas,andinculturedcells,chloramphenicolresistance.Thissequenceofdiscoveryistheopposite,forthemostpart, ofthatpursuedtodateinthedelineationofthenucleargenomewheretheprogressionhasbeenfromstudyofdis-eases,thentotheirmapping,andfinallytothesequencingofthegenes.Themitochondrialchromosome,withitsmere16,569basepairs,canbeconsideredaparadigmforwhatthehumangenomeproject(seelater)hopestoachieveforthe nucleargenome(whichisapproximately200,000timeslargerintermsofnucleotides).Indeed,completesequencingmayhelpgreatlyinidentifyingallthenucleargenesjustasitdidinthecaseofthemitochondrialgenes.Presentlywehaveinformation,ascataloguedinMendelianInheritanceinMan(8),ononlyabout5000ofthe50,000to100,000genes, orgeneloci(Fig.4).WalterGilbertsuggestedthatcompletesequencingmaybethebestwaytofindtherest.Thereafter,onecandeterminethefunctionofthegenesandthedis-orderscausedbymutationstherein,ashasbeendoneforthemitochondrialchromosome. OTHERTYPESOFMAPSGenemappingsubsumesbothgeneticlinkagemaps,whicharederivedfrommeioticrecombinationfrequenciesandmeasuredincentimorgans,andphysicalmaps,basedonvar-iousexperimentalmethodsofwhichseveralhavebeende-scribedearlier.Asdiscussedelsewhere,thelargefragment clonesthatareproducedbyYACcloningpermitthecreationofcontigmapsforeachchromosome,i.e.,mapsofoverlap-ping,andthereforecontiguous,DNAsegments.Smallersegments,cosmidclones,havebeenusedforthesamepur-posebutarelessefficient.Asalreadyindicated,thesemappedsegmentscanbeusedformappinggenesofun- knownlocationbyhybridization.Theyarealsotherawmaterialfornucleotidesequencing.Thecontigmapisthepenultimatephysicalmap;thenucleotidesequenceistheul-timatemap.Thecorrelationofthegeneticmap(basedonthelocationofclonedgenesthroughfamilylinkagestudies)andthephys- icalmap(asrepresentedbythecontigmap,forexample)islikelytobeaidedbytheuseofSTSs(sequence-taggedsites)(19).Theymayobviate,toaconsiderableextent,theneedtostoreanddistributeclonedDNAsegmentsforstudybyin-vestigatorsinmanylaboratories.KnowingtheSTSidentifierofaparticularsegment,theresearchercanclonethatseg- mentandnotrequireitasaclonefromarepository.Onewillstoreinformation,notDNA,relatedtoeachpartofthegenome.STSsareasortofEsperantoforthescientistsusingdiversegeneticandphysicalmethods.FindingallthegenescouldbehelpedbyaconcertedefforttocreatethecDNAmap -themapofprobesmadebyre-versetranscriptionofmessengerRNAsthathavetissueanddevelopmentalstagespecificity.TheeDNA(orexon)mapwouldprovidecandidategenesfordiseasesmappedbyphenotype.Becausebydefinitiontheexonsarewheretheac-tionis,sequencingcouldlogicallyandefficientlystartwith them.THEHUMANGENOMEPROJECTThehumangenomeinitiativeaimstomapandsequencecompletelythehumangenome.Thesequenceistheultimate MAPPINGHUMANGENES 19 map.TheNRC/NAScommittee,whichconcludedthattheHumanGenomeProjectwasworthwhileandcouldbedoneinareasonabletimeframeandbudget,suggested?mapfirst,sequencelater?(20).Noabsolutestepwisedichotomywasinthemindofthecommittee,butthisorderwasconsideredad-visablebecauseboththegenemapandthecontigmapare necessaryformostefficientsequencing,andthetechnologyforsequencingrequiresimprovement.Givenadequatefunding(anestimated$200millionayearfortheworldwideeffort,in1988dollars),thehumangenomeprojectshouldbecompletedin15years.Spin-offinapplica-tionstomedicine,inparticular,occurscontinuouslyduring thatperiod.Itiswelltobeawareoftheend-productoftheproject:Itwillproduceareferencemap(andsequence)-asourcebookforhumanbiologyandmedicineforcenturiestocome.Twobroadareaswilloccupyscientistsformanyyears:variationandfunction.Itisurgedbysomethatstudiesofvariationinpopulationsworldwideshouldbeginimmedi- ately.Importantasthesestudiesare,itseemsthattheextentofvariationisnotsuchthatconfusionwillariseinassemblingthereferencemap.Thejournalists?questionisirrelevant,Whosegenomewillbemappedandsequenced?AlthoughthesourceofDNAusedinsequencingshouldberecorded,thefinalmapandsequencewillbeacompositeofinforma- tionfrommanyindividuals.Theextentofvariationwillneedtobestudiedlater.Itandfunctionareallofbiologyandgenetics;itisunreasonabletoexpectthehumangenomeprojecttodoitallanditwouldbeimprudentfortheeffortofthehumangenomeprojecttobediffuse.Itwillbeimpor-tantto?keepoureyesontheball?ifthemainobjectiveofa completemapandsequenceistobeachievedinatimelymannerandwithinthebudgetlimitsset.Itisprojectedthatdoingtheentirejobwillrepresenteconomyofscaleandhavingthemap/sequenceinformationwillfacilitategreatlytheelucidationofgeneticdisease.Cysticfibrosisisanexam-ple:identificationofthegenewasanexpensiveproject(how expensiveisdifficulttoestimateprecisely)andwouldun-doubtedlyhavebeenmuchlessexpensive(howmuchlessisalsohardtosay)ifthecompletesequencewereavailable.COUNTER-ARGUMENTSANDCOUNTER-COUNTER-ARGUMENTSCONCERNINGTHEHUMANGENOMEPROJECT Amongscientists,themainargumentsagainsttheHumanGenomeProjectseemtobefour:thatitisbadscience;thatitisbigscience(withtheimplicationthatitisnotthewayscienceismosteffectivelydone);thatitcreatesanimpropermilieufordoctoraltraininginscience;andthatitistakingmoneyawayfromotherworthy(intheopinionofsome, moreworthy)projects.4ThepurposeoftheHGPistocreateatoolforscience-thesourcebookreferredtoearlier.AgooddealofappliedscienceandengineeringwillgointotheHGP,butitmaynotbeappropriatetocriticizetheprojectthroughacomparisonwithbiologicalscienceasithasbeenpursuedtraditionally. TheHGPisnotsomuchbigscienceasitiscoordinated,interdisciplinaryscience.Especiallyinthesequencingpartoftheproject,boththegenerationofthedataandparticu-larlytheirinterpretationwillrequiretherecruitmentofex-pertsfromdisciplinesthathavehadlittleinvolvementinbiologytodate.Itseemsclearthathandlingtheinformation,validating,storing,andretrieving it,searchingitforpatternsindicativeoffunctionaldomains,andidentifyingthecodingportions,willrequiremuchcomputer-assistedexpertise.Itrepresentsaformidablechallengetotheinformationscientist. Totheargumentthataninstitutionwheregenomics(agenerictermformappingandsequencing)isbeingdoneisapoorsiteforgraduatetrainingandthattheHGPwillhaveamajoradverseeffectongraduateprogramsinbiology,real-itymaybequitethecontrary.Withthefullmapandse-quence,graduatestudentswillbesparedthedrudgeryofcloningandsequencing particulargenesbeforetheycangetdowntothemuchmoreinterestingandintellectuallyde-mandingworkofstudyingvariation,function,regulation,andsoon.Thegenomicslaboratorieswillbesuperbsettingsfortraininganewbreedofscientist-onewhoispreparedtocapitalizeonboththemoleculargeneticsrevolutionand thecomputationrevolution.Thesewillbetheleadersinbiol-ogyinthe21stcentury.ItappearsthattheHGPisbeingmadeascapegoatbythosefrustratedbythetightfundingforresearch.IftheHGPwentawaycompletely,thefundingsituationwouldnotchangeperceptibly.Indeed,theexcitementstimulatedby discussionoftheHGPhashadandcancontinuetohaveabeneficialeffectonsciencefundinggenerally.[]REFERENCES 1.Wilson,E.B.(1911)Thesexchromosomes.Arch.Mikrosk.Anat.Enwicklungsmech.77,249-2712.Homer,J.F.(1876)DieErblichkeitdesDaltonismus.Amtl.Ber.UeberdieVerwaltungdesMedizinaiwesensdesKi.Zuricho.Jahre1876.31,208-2113.Haldane,J.B.S.,Sprunt,A.D.,andHaldane,N.M.(1915)Reduplicationinmice.(Preliminarycommunication.)J. Genet.5,133-1354.Ott,J.(1985)AnalysisofHumanGeneticLinkage.TheJohnsHop-kinsUniv.Press,Baltimore5.Donahue,R.P.,Bias,W.B.,Renwick,J.H.,andMcKusick,V.A.(1968)ProbableassignmentoftheDuffybloodgrouplocustochromosome 1inman.Proc.NaiLAcad.Sci.USA61,949-9556.Botstein,D.,White,R.L.,Skolnick,M.,andDavis,R.W.(1980)Constructionofageneticlinkagemapinmanusingre-strictionlengthpolymorphisms.Am.jHum.Genet.32,314-3317.Roberts,L.(1990)Thewormproject.&ience248,1310-13138.McKusick,V.A.(1990)Mendelianinheritanceinman:cata- logsofautosomaldominant,autosomalrecessive,andX-linkedphenotypes,9thed.JohnsHopkinsUniversityPress,Baltimore9.Fan,Y.-s.,Davis,L.M.,andShows,T.B.(1990)MappingsmallDNAsequencesbyfluorescenceinsituhybridizationdirectlyonbandedmetaphasechromosomes.Proc.Nati.Acad.Sci.USA87,6223-622710.Lawrence,J.B.,Villnave,C.A.,andSinger,R.H.(1988)Sen- sitivehighresolutionchromatinandchromosomemappinginSitu:presenceandorientationofcloselyintegratedcopiesofEBVinalymphomacellline.Cell52,51-5611.Boehnke,M.,Amnheim,N.,Li,H.,andCollins,F.S.(1989)Fine-structuregeneticmappingofhumanchromosomesusingthepolymerasechainreactiononsinglesperm:experimentaldesignconsiderations. Am.jHum.Genet.45,21-3212.Cui,X.,Li,H.,Goradia,T.M.,Lange,K.,Kazazian,H.H.,Jr.,Galas,D.,andArnheim,N.(1989)Single-spermtyping:de-terminationofgeneticdistancebetweentheG-gamma-globinandparathyroidhormonelocibyusingthepolymerasechainreactionandallele-specificoligomers.Proc.Nail.Acad.&i.USA86,9389-9393 amindebtedtoLeroyE.Hoodforthislistingofcounterargu-mentsand,inpart,fortheformulationofcounter-counter-arguments. 20Vol.5January1991 TheFASEBJournal McKUSICK 13.Lander,E.S.,andBotstein,D.(1987)Homozygositymapping:awaytomaphumanrecessivetraitswiththeDNAofinbredchildren.Science.235,1567-157014.Taylor,B.A.(1989)Recombinantinbredstrains.InGeneticVari-antsandStrainsoftheLaboratoryMouse,2nded.(Lyon,M.,andSearle,A.G.,eds)OxfordUniversityPress,NewYork 15.Goss,S.J.,andHarris,H.(1975)Newmethodformappinggenesinhumanchromosomes.Nature(London)255,680-68416.Cox,D.R.,Pritchard,C.A.,Uglum,E.,Gashere,D.,Kobori,J.,andMeyers,R.M.(1989)SegregationoftheHuntingtondiseaseregionofhumanchromosome4inasomaticcellhybrid.Genomics4,397-40717.Goodfellow,P.J., Povey,S.,Nevanlinna,H.A.,andGoodfellow,P.N.(1990)Generationofapanelofsomaticcellhybridscon- tamingunselectedfragmentsofhumanchromosome10byX-rayirradiationandcellfusion:applicationtoisolatingtheMEN2Aregioninhybridcells.Somat.CellMol.Genet.16,163-17118.McKusick,V.A.Themorbidanatomyofthehumangenome:areviewofgenemappinginclinicalmedicine.Medicine65, 1-33,1986;66,1-63,237-296,1987;67,1-19,198819.Olson,M.,Hood,L.,Cantor,C.,andBotstein,D.(1989)Acommonlanguageforphysicalmappingofthehumangenome.Science245,1434-143520.NationalResearchCouncil(1988)CommitteeonMappingandSequencingtheHumanGenome:mappingandsequencingthe humangenome.NationalAcademyPress,Washington,D.C. 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Genetics
Gene Inheritance and Transmission
Gene Expression and Regulation
Nucleic Acid Structure and Function
Chromosomes and Cytogenetics
Evolutionary Genetics
Population and Quantitative Genetics
Genomics
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