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FigureFigureConcept14.1:MendelusedConcept14.1:Mendelusedtheapproachtoidentifytwolawsof•MendeldiscoveredthebasicprinciplesofhereditybybreedinggardenpeasincarefullyplannedexperimentsMendel’sExperimental,QuantitativeMendel’sExperimental,QuantitativeAdvantagesofpeaplantsforgeneticTherearemanyvarietieswithdistinctheritablefeatures,orcharacters(suchasflowercolor);charactervariants(suchaspurpleorwhiteflowers)arecalledtraitsMatingcanbeEachflowerhassperm-producingorgans(stamens)andegg-producingorgan(carpel)Cross-pollination(fertilizationbetweendifferentplants)involvesdustingoneplantwithpollenfromanother•Figure123Figure12345Firstfilial•Mendelchosetotrackonlythosecharactersthatoccurred•MendelchosetotrackonlythosecharactersthatoccurredintwodistinctalternativeformsHealsousedvarietiesthattrue-breeding纯育生(plantsthatproduceoffspringofthesamevarietywhentheyself-pollinate)••Inatypicalexperiment•InatypicalexperimentMendelmatedtwocontrasting,true-breedingvarieties,aprocesscalledhybridization杂交orThetrue-breedingparentsarethePgeneration亲代ThehybridoffspringofthePgenerationarecalledtheF1generation子代(filial)WhenF1individualsself-pollinateorcross-pollinatewithotherF1hybrids,theF2generationisproduced•••TheLawofSegregation分TheLawofSegregation分离定•WhenMendelcrossedcontrasting,true-breedingwhite-andpurple-floweredpeaplants,alloftheF1hybridswerepurpleWhenMendelcrossedtheF1hybrids,manyoftheF2plantshadpurpleflowers,butsomehadwhiteMendeldiscoveredaratioofaboutthreetoone,purpletowhiteflowers,intheF2••Figure14.3-PGenerationFigure14.3-PGenerationFigure14.3-PGenerationFigure14.3-PGenerationAllplantshadpurpleSelf-orcross-Figure14.3-PGenerationFigure14.3-PGenerationAllplantshadpurpleSelf-orcross-F2•Mendelreasonedthatonlythepurpleflowerfactorwasaffectingflower•MendelreasonedthatonlythepurpleflowerfactorwasaffectingflowercolorintheF1hybridsMendelcalledthepurpleflowercolor•andtheflowercolorarecessivetrait隐形特ThefactorforwhiteflowerswasnotdilutedordestroyedbecauseitreappearedintheF2generation•Mendelobservedthesamepatternofinheritanceinsixotherpeaplantcharacters,eachrepresentedbyMendelobservedthesamepatternofinheritanceinsixotherpeaplantcharacters,eachrepresentedbytwotraitsWhatMendelcalleda“heritablefactor”iswhatwenowcallagene••©2011PearsonEducation,TableTableMendel’sMendeldevelopedaMendel’sMendeldevelopedahypothesistoexplainthe3:1inheritancepatternheobservedinF2offspringFourrelatedconceptsmakeupthisTheseconceptscanberelatedtowhatwenowknowaboutgenesandchromosomes•••©2011PearsonEducation,•First:alternativeversionsofgenesaccountforvariationsininherited•First:alternativeversionsofgenesaccountforvariationsininheritedForexample,thegeneforflowercolorinpeaplantsexistsintwoversions,oneforpurpleflowersandtheotherforwhiteThesealternativeversionsofagenearenowcalledalleles等位基因Eachgeneresidesataspecificlocusonaspecificchromosome基因座•••FigureAlleleforpurpleFigureAlleleforpurplePairofLocusforflower-colorAlleleforwhite•Second:foreachcharacter,anorganisminheritstwoalleles,one•Second:foreachcharacter,anorganisminheritstwoalleles,onefromeachparentMendelmadethisdeductionwithoutknowingabouttheroleofchromosomesThetwoallelesataparticularlocusmaybeidentical,asinthetrue-breedingplantsofMendel’sPgenerationAlternatively,thetwoallelesatalocusmaydiffer,asintheF1hybrids••••Third:ifthe•Third:ifthetwoallelesatalocusdiffer,thenone(thedominantallele)determinestheorganism’sappearance,andtheother(therecessiveallele)hasnonoticeableeffectonappearanceIntheflower-colorexample,theF1plantshadpurpleflowersbecausethealleleforthattraitisdominant••Fourth:(nowknownasthelawofsegregation):thetwo•Fourth:(nowknownasthelawofsegregation):thetwoallelesforaheritablecharacterseparate(segregate)duringgameteformationandendupindifferentThus,aneggoraspermgetsonlyoneofthetwoallelesthatarepresentintheThissegregationofallelescorrespondstothedistributionofhomologouschromosomestodifferentgametesin•••Mendel’ssegregationmodelaccounts•Mendel’ssegregationmodelaccountsforthe3:1ratioheobservedintheF2generationofhisnumerouscrossesThepossiblecombinationsofspermandeggcanbeshownusingaPunnettsquare庞氏表,adiagramforpredictingtheresultsofageneticcrossbetweenindividualsofknowngeneticmakeupAcapitalletterrepresentsadominantallele,andalowercaseletterrepresentsarecessiveallele••Figure14.5-PFigure14.5-PGeneticmakeup:PurpleflowersWhitePpFigure14.5-PGeneticmakeup:PurpleflowersFigure14.5-PGeneticmakeup:PurpleflowersWhitePpF1Geneticmakeup:PurplepPFigure14.5-PGeneticmakeup:PurpleflowersWhitePpF1Figure14.5-PGeneticmakeup:PurpleflowersWhitePpF1Geneticmakeup:PurplepPSpermfromF1(Pp)F2pPPEggsfromF1(Pp)plantp3:UsefulGenetic•AnorganismwithtwoidenticalallelesforaUsefulGenetic•Anorganismwithtwoidenticalallelesforacharacterissaidtobehomozygous纯合forthegenecontrollingthatcharacterAnorganismthathastwodifferentallelesforageneissaidtobeheterozygous杂合forthegenecontrollingthatcharacterUnlikehomozygotes,heterozygotesarenottrue-breeding•••Becauseofthedifferenteffectsofdominantandrecessivealleles,anorganism’straitsdonotalways•Becauseofthedifferenteffectsofdominantandrecessivealleles,anorganism’straitsdonotalwaysrevealitsgeneticcompositionTherefore,wedistinguishbetweenanorganism’sphenotype表型,orphysicalappearanceanditsgenotype基因型orgeneticmakeupIntheexampleofflowercolorinpeaplants,PPandPpplantshavethesamephenotype(purple)butdifferentgenotypes••Figure132Figure13211RatioRatioTheTestcross测•HowcanwetellthegenotypeofanindividualwithTheTestcross测•Howcanwetellthegenotypeofanindividualwiththedominantphenotype?SuchanindividualcouldbeeitherhomozygousdominantorheterozygousTheansweristocarryoutatestcross:breedingthemysteryindividualwithahomozygousrecessiveindividualIfanyoffspringdisplaytherecessivephenotype,themysteryparentmustbe•••Figureunknowngenotype:PPorPp?parentisPPknowngenotype:parentisPppFigureunknowngenotype:PPorPp?parentisPPknowngenotype:parentisPpppppPPPpAlloffspringoffspringpurpleoffspringTheLawofIndependentTheLawofIndependent•MendelderivedthelawofsegregationbyfollowingasinglecharacterTheF1offspringproducedinthiscrossweremonohybrids单因子杂交,individualsthatareheterozygousforoneAcrossbetweensuchheterozygotesiscalledamonohybridcross•••Mendelidentifiedhissecondlawofinheritancebyfollowingtwo•MendelidentifiedhissecondlawofinheritancebyfollowingtwocharactersatthesametimeCrossingtwotrue-breedingparentsdifferingintwocharactersproducesdihybridsintheF1generation,heterozygousforbothAdihybridcross,acrossbetweenF1dihybrids,candeterminewhethertwocharactersaretransmittedtooffspringasapackageorindependently••FigurePF1HypothesisofHypothesisofoffspringofFigurePF1HypothesisofHypothesisofoffspringofPhenotypicratioPhenotypicratioPhenotypicratioapproximately•Usingadihybridcross,•Usingadihybridcross,MendeldevelopedthelawofindependentassortmentThelawofindependentassortmentstatesthateachpairofallelessegregatesindependentlyofeachotherpairofallelesduringgameteformationStrictlyspeaking,thislawappliesonlytogenesondifferent,nonhomologouschromosomesorthosefarapartonthesameGeneslocatedneareachotheronthesamechromosometendtobeinheritedtogether•••Concept14.2:ThelawsofConcept14.2:ThelawsofprobabilityMendelian•Mendel’slawsofsegregationandindependentassortmentreflecttherulesofWhentossingacoin,theoutcomeofonetosshasnoimpactontheoutcomeofthenexttossInthesameway,theallelesofonegenesegregateintogametesindependentlyofanothergene’salleles••TheMultiplicationandAdditionTheMultiplicationandAdditionAppliedtoMonohybrid•Themultiplicationrulestatesthattheprobabilitythattwoormoreindependenteventswilloccurtogetheristheproductoftheirindividualprobabilities相乘法則ProbabilityinanF1monohybridcrosscanbedeterminedusingthemultiplicationruleSegregationinaheterozygousplantislikeflippingacoin:Eachgametehasa½chanceofcarryingthedominantalleleanda½chanceofcarryingtherecessiveallele••FigureSegregationofallelesintoeggsSegregationofallelesintospermrRRRRFigureSegregationofallelesintoeggsSegregationofallelesintospermrRRRRrRrrrRr•Theadditionrulestatesthattheprobabilitythatanyoneoftwoormoreexclusiveevents•Theadditionrulestatesthattheprobabilitythatanyoneoftwoormoreexclusiveeventswilloccuriscalculatedbyaddingtogethertheirindividualprobabilities相加法則TheruleofadditioncanbeusedtofigureouttheprobabilitythatanF2plantfromamonohybridcrosswillbeheterozygousratherthanhomozygous•SolvingComplexGeneticsProblemswithSolvingComplexGeneticsProblemswithRulesof•WecanapplythemultiplicationandadditionrulestopredicttheoutcomeofcrossesinvolvingmultiplecharactersAdihybridorothermulticharactercrossisequivalenttotwoormoreindependentmonohybridcrossesoccurringsimultaneouslyIncalculatingthechancesforvariousgenotypes,eachcharacterisconsideredseparately,andthentheindividualprobabilitiesaremultiplied••FigureProbabilityofYYRR1/FigureProbabilityofYYRR1/4(probabilityofProbabilityof1/2Figure1/4(probabilityofFigure1/4(probabilityofpp)1/2(yy)6/16or1/21/41/21/21/21/41/21/41/2ChanceofatleasttworecessiveConcept14.3:InheritancepatternsaremoreConcept14.3:InheritancepatternsaremorecomplexthanpredictedbysimpleMendeliangenetics•TherelationshipbetweengenotypeandphenotypeisrarelyassimpleasinthepeaplantcharactersMendelstudied•ManyheritablearedeterminedbyonlyonegenewithtwoHowever,thebasicprinciplesofsegregationandindependentassortmentapplyeventomorecomplexpatternsofinheritance•ExtendingMendelianGeneticsforExtendingMendelianGeneticsfora•InheritanceofcharactersbyasinglegenemaydeviatefromsimpleMendelianpatternsinthefollowingsituations:WhenallelesarenotcompletelydominantorrecessiveWhenagenehasmorethantwoWhenageneproducesmultipleDegreesof•Completedominance完全Degreesof•Completedominance完全occurswhenphenotypesoftheheterozygoteanddominanthomozygoteareInincompletedominance不完全显性,thephenotypeofF1hybridsissomewherebetweenthephenotypesofthetwoparentalIncodominance共同显性twodominantallelesaffectthephenotypeinseparate,distinguishableways••PPPPF1PPTheRelationBetweenDominanceTheRelationBetweenDominance•Adominantalleledoesnotsubduearecessiveallele;allelesdon’tinteractthatAllelesaresimplyvariationsinagene’snucleotidesequenceForanycharacter,dominance/recessivenessrelationshipsofallelesdependonthelevelatwhichweexaminethephenotype•••Tay-Sachsdiseaseisfatal;adysfunctionalenzymecausesanaccumulation•Tay-Sachsdiseaseisfatal;adysfunctionalenzymecausesanaccumulationoflipidsinthebrainAttheorganismallevel,thealleleisAtthebiochemicallevel,thephenotype(i.e.,theenzymeactivitylevel)isincompletelyAtthemolecularlevel,theallelesareFrequencyofDominant•DominantFrequencyofDominant•DominantallelesarenotnecessarilymorecommoninpopulationsthanrecessiveForexample,onebabyoutof400intheUnitedStatesisbornwithextrafingersor•©2011PearsonEducation,•Theallelefor•ThealleleforthisunusualtraitisdominanttothealleleforthemorecommontraitoffivedigitsperappendageInthisexample,therecessivealleleisfarmoreprevalentthanthepopulation’sdominantallele•Multiple•MostgenesexistinpopulationsMultiple•Mostgenesexistinpopulationsinmorethantwoallelicforms•Forexample,fourphenotypesofthebloodgroupinhumansaredeterminedthreeallelesfortheenzyme(I)thatattachesAorBcarbohydratestoredbloodcells:IA,IB,andi.TheenzymeencodedbytheIAalleleaddstheAcarbohydrate,whereastheenzymeencodedbytheIBalleleaddstheBcarbohydrate;theenzymeencodedbytheialleleaddsneither•Figure(a)ThethreeallelesfortheABObloodgroupsandtheirFigure(a)ThethreeallelesfortheABObloodgroupsandtheiriAB(b)BloodgroupgenotypesandororRedbloodcellABOPleiotropy基因多效性•MostgenesPleiotropy基因多效性•Mostgeneshavemultiplephenotypiceffects,apropertycalledpleiotropyForexample,pleiotropicallelesareresponsibleforthemultiplesymptomsofcertainhereditarydiseases,suchascysticfibrosis囊胞性纤维症andsickle-celldisease镰刀型红血球疾•MolecularGeneticsandGeneLocus:MolecularGeneticsandGeneLocus:7q31.2-TheCFTRgeneisfoundinregionq31.2onthelong(q)armofhumanchromosome7.GeneStructure:Thenormalallelicvariantforthisgeneisabout250,000bplongandcontains27mRNA:Theintron-freemRNAtranscriptfortheCFTRgeneis6129bplong.CodingSequence(CDS):4443bpwithinthemRNAcodefortheaminoacidsequenceofthegene'sproteinproduct.ProteinSize:TheCFTRproteinis1480aminoacidslongandhasamolecularweightof168,173ProteinFunction:ThenormalCFTRproteinproductisachloridechannelproteinfoundinmembranesofcellsthatlinepassagewaysofthelungs,liver,pancreas,intestines,reproductivetract,andskin.CFTRisalsoinvolvedintheregulationofothertransportpathways.AssociatedDisorders:Defectiveversionsofthisprotein,causedbyCFTRgenemutations,canleadtothedevelopmentofcysticfibrosis(CF)andcongenitalbilateralaplasiaofthevasdeferens•••••••ProteinCFTRcontrolschlorideionmovementProteinCFTRcontrolschlorideionmovementinandoutofthecell.•nandProteinFunctionProteinFunctionProteinStructureandCFTRtransportschlorideions(Cl-)ionsacrossProteinStructureandCFTRtransportschlorideions(Cl-)ionsacrossthemembranesofcellsinthelungs,liver,pancreas,digestivetract,reproductivetract,andskin.CFTRismadeupoffive••–twomembrane-spanningdomains(MSD1andMSD2)thatformthechlorideionchanneltwonucleotide-bindingdomains(NBD1andNBD2)thatbindandhydrolyzeATP(adenosinetriphosphate)andaregulatory(R)––DeltaF508,themostcommonCF-causingmutation,occursintheDNAsequencethatcodesforthefirstnucleotide-bindingdomain•ChangesinProteinChangesinProtein•CFTRfunctionsprincipallyasacAMP-inducedchloridechannelandappearscapableofregulatingotherionchannels.Besidesthemostcommonmutation,ΔF508,accountingforabout70%ofCFchromosomesworldwide,morethan850mutantalleleshavebeenreportedtotheCFGeneticAnalysisThesemutationsaffectCFTRthroughavarietyofmolecularmechanismswhichcanproducelittleornofunctionalCFTRattheapicalmembrane.••ExtendingMendelianGeneticsExtendingMendelianGeneticsforTwoMoreSometraitsmaybedeterminedbytwoormoregenes©2011PearsonEducation,Epistasis•Inepistasis,aEpistasis•Inepistasis,ageneatonelocusaltersthephenotypicexpressionofageneatasecondlocusForexample,inLabradorretrieversandmanyothermammals,coatcolordependsontwogenesOnegenedeterminesthepigmentcolor(withallelesBforblackandbforbrown)Theothergene(withallelesEforcolorandefornocolor)determineswhetherthepigmentwillbedepositedinthehair•••FigureFigure:39:4EpistasisEpistasisInheritance多基因遗传•QuantitativeInheritance多基因遗传•QuantitativecharactersarethosethatvaryinthepopulationalongacontinuumQuantitativevariationusuallyindicatespolygenicinheritance,anadditiveeffectoftwoormoregenesonasinglephenotypeSkincolorinhumansisanexampleofpolygenicinheritance••FigureFigure8Numberdark-skin0156234NatureandNurture:TheNatureandNurture:TheImpacton•AnotherdeparturefromMendeliangeneticsariseswhenthephenotypeforacharacterdependsonenvironmentaswellasgenotypeThenormofreaction反应范isthephenotypicrangeofagenotypeinfluencedbytheenvironmentForexample,hydrangeaflowers绣ofthesamegenotyperangefromblue-violettopink,dependingonsoilacidity••FigureBasicFigureBasicAcidic•Normsofreaction•NormsofreactionaregenerallybroadestforpolygeniccharactersSuchcharactersarecalledmultifactorialbecausegeneticandenvironmentalfactorscollectivelyinfluencephenotype•IntegratingaMendelianViewofIntegratingaMendelianViewofand•Anorganism’sphenotypeincludesitsphysicalappearance形态internalanatomy组织生理andbehavior行•Anorganism’sphenotypereflectsitsoverallgenotypeanduniqueenvironmentalhistoryConcept14.4:ManyhumanConcept14.4:ManyhumantraitsMendelianpatternsof•HumansarenotgoodsubjectsforgeneticresearchGenerationtimeistooParentsproducerelativelyfewBreedingexperimentsareHowever,basicMendeliangeneticsenduresasthefoundationofhuman•PedigreeAisafamilyPedigreeAisafamilytree家describestheinterrelationshipsofparentsandchildrenacrossgenerationsInheritancepatternsofparticulartraitscanbetracedanddescribedusing•FigureFForFigureFForb)Isanattachedearlobeadominantorrecessivetrait?(a)Isawidow’speakadominantorrecessivetrait?•Pedigreescanalso•PedigreescanalsobeusedtomakepredictionsaboutfutureoffspringWecanusethemultiplicationandadditionrulestopredicttheprobabilityofspecificphenotypes•RecessivelyInherited•ManyRecessivelyInherited•ManygeneticdisordersareinheritedinarecessivemannerTheserangefromrelativelymildtolife-•TheBehaviorofRecessive•RecessivelyinheriteddisordersshowuponlyinindividualsTheBehaviorofRecessive•Recessivelyinheriteddisordersshowuponlyinindividualshomozygousfortheallele•Carriersareindividualswhocarrytherecessiveallelebutarephenotypicallynormal;mostindividualswithrecessivedisordersareborntocarrierisarecessive•Albinism白化characterizedbyalackofpigmentationinskinandhair©2011PearsonEducation,FigureaAAFigureaAAa•Ifarecessiveallelethatcausesadiseaseisrare,thenthe•Ifarecessiveallelethatcausesadiseaseisrare,thenthechanceoftwocarriersmeetingandmatingislow•Consanguineousmatings同族婚matingsbetweencloseincreasethechanceofmatingbetweentwocarriersofthesamerarealleleMostsocietiesandcultureshavelawsortaboosagainstmarriagesbetweenclose•CysticCysticfibrosisisthemostcommonlethalgeneticdiseaseCysticCysticfibrosisisthemostcommonlethalgeneticdiseaseintheUnitedStates,strikingoneoutofevery2,500peopleofEuropeanThecysticfibrosisalleleresultsindefectiveorabsentchloridetransportchannelsinplasmamembranesleadingtoabuildupofchlorideionsoutsidethecellSymptomsincludemucusbuildupinsomeinternalorgansandabnormalabsorptionofnutrientsinthesmallintestine•••Sickle-CellDisease:AGeneticDisorderSickle-CellDisease:AGeneticDisorderEvolutionary•Sickle-celldiseaseaffectsoneoutof400ThediseaseiscausedbythesubstitutionofasingleaminoacidinthehemoglobinproteininredbloodcellsInhomozygousindividuals,allhemoglobinisabnormal(sickle-cell)Symptomsincludephysicalweakness,pain,organdamage,andevenparalysis•••Fig.14-•Heterozygotes(saidtohavesickle-celltrait)areFig.14-•Heterozygotes(saidtohavesickle-celltrait)areusuallyhealthybutmaysuffersomesymptomsAboutoneoutoftenAfricanAmericanshassicklecelltrait,anunusuallyhighfrequencyofanallelewithdetrimentaleffectsinhomozygotesHeterozygotesarelesssusceptibletothemalariaparasite,sothereisanadvantagetobeingheterozygous••DominantlyInherited•SomehumanDominantlyInherited•SomehumandisordersarecausedbydominantallelesDominantallelesthatcausealethaldiseasearerareandarisebymutationAchondroplasia软骨发育不全isaformofdwarfismcausedbyararedominant••FigureDdFigureDdddHuntington’sDisease:ALate-Onset•TheHuntington’sDisease:ALate-Onset•Thetimingofonsetofadiseasesignificantlyaffectsitsinheritance•Huntington’sdiseaseisdegenerativediseaseofthenervousThediseasehasnoobviousphenotypiceffectsuntiltheindividualisabout35to40yearsofOncethedeteriorationofth