孟德爾及其基因觀念課件

孟德爾及其基因觀念Overview:DrawingfromtheDeckofGenesWhatgeneticprinciplesaccountforthepassingoftraitsfromparentstooffspring?The“blending”hypothesisistheideathatgeneticmaterialfromthetwoparentsblendstogether(likeblueandyellowpaintblendtomakegreen)混生假說Copyright?2008PearsonEducationInc.,publishingasPearsonBenjaminCummingsThe“particulate”hypothesisistheideathatparentspassondiscreteheritableunits(genes)MendeldocumentedaparticulatemechanismthroughhisexperimentswithgardenpeasCopyright?2008PearsonEducationInc.,publishingasPearsonBenjaminCummingsFig.14-1Concept14.1:MendelusedthescientificapproachtoidentifytwolawsofinheritanceMendeldiscoveredthebasicprinciplesofhereditybybreedinggardenpeasincarefullyplannedexperimentsCopyright?2008PearsonEducationInc.,publishingasPearsonBenjaminCummingsMendel’sExperimental,QuantitativeApproachAdvantagesofpeaplantsforgeneticstudy:Therearemanyvarietieswithdistinctheritablefeatures,orcharacters特徵

(suchasflowercolor);charactervariants(suchaspurpleorwhiteflowers)arecalledtraits性狀MatingofplantscanbecontrolledEachpeaplanthassperm-producingorgans(stamens)andegg-producingorgans(carpels)Cross-pollination(fertilizationbetweendifferentplants)canbeachievedbydustingoneplantwithpollenfromanotherCopyright?2008PearsonEducationInc.,publishingasPearsonBenjaminCummingsFig.14-2TECHNIQUERESULTSParentalgeneration(P)StamensCarpel1234Firstfilialgener-ationoffspring(F1)5Fig.14-2aStamensCarpelParentalgeneration(P)TECHNIQUE1234Fig.14-2bFirstfilialgener-ationoffspring(F1)RESULTS5Mendelchosetotrackonlythosecharactersthatvariedinaneither-ormannerHealsousedvarietiesthatwere

true-breeding(plantsthatproduceoffspringofthesamevarietywhentheyself-pollinate)純系培養(yǎng)Copyright?2008PearsonEducationInc.,publishingasPearsonBenjaminCummingsInatypicalexperiment,Mendelmatedtwocontrasting,true-breedingvarieties,aprocesscalledhybridization雜交Thetrue-breedingparentsarethePgeneration

親代ThehybridoffspringofthePgenerationarecalledtheF1generation

第一子代WhenF1individualsself-pollinate,theF2generation

isproduced第二子代Copyright?2008PearsonEducationInc.,publishingasPearsonBenjaminCummingsTheLawofSegregation分離率WhenMendelcrossedcontrasting,true-breeding

whiteandpurplefloweredpeaplants,alloftheF1hybridswerepurpleWhenMendelcrossedtheF1hybrids,manyoftheF2plantshadpurpleflowers,butsomehadwhiteMendeldiscoveredaratioofaboutthreetoone,purpletowhiteflowers,intheF2generationCopyright?2008PearsonEducationInc.,publishingasPearsonBenjaminCummingsFig.14-3-1EXPERIMENTPGeneration(true-breedingparents)Purpleflowers

Whiteflowers

Fig.14-3-2EXPERIMENTPGeneration(true-breedingparents)Purpleflowers

Whiteflowers

F1Generation(hybrids)AllplantshadpurpleflowersFig.14-3-3EXPERIMENTPGeneration(true-breedingparents)Purpleflowers

Whiteflowers

F1Generation(hybrids)AllplantshadpurpleflowersF2Generation705purple-floweredplants224white-floweredplantsMendelreasonedthatonlythepurpleflowerfactorwasaffectingflowercolorintheF1hybridsMendelcalledthepurpleflowercoloradominanttraitandthewhiteflowercolorarecessivetraitMendelobservedthesamepatternofinheritanceinsixotherpeaplantcharacters,eachrepresentedbytwotraitsWhatMendelcalleda“heritablefactor”遺傳因子iswhatwenowcallagene基因Copyright?2008PearsonEducationInc.,publishingasPearsonBenjaminCummingsTable14-1Mendel’sModelMendeldevelopedahypothesistoexplainthe3:1inheritancepatternheobservedinF2offspringFourrelatedconceptsmakeupthismodelTheseconceptscanberelatedtowhatwenowknowaboutgenesandchromosomesCopyright?2008PearsonEducationInc.,publishingasPearsonBenjaminCummingsThefirstconceptisthatalternativeversions

ofgenesaccountforvariationsininheritedcharactersForexample,thegeneforflowercolorinpeaplantsexistsintwoversions,oneforpurpleflowersandtheotherforwhiteflowersThesealternativeversionsofagenearenowcalledalleles對偶EachgeneresidesataspecificlocusonaspecificchromosomeCopyright?2008PearsonEducationInc.,publishingasPearsonBenjaminCummingsFig.14-4AlleleforpurpleflowersHomologouspairofchromosomesLocusforflower-colorgeneAlleleforwhiteflowersThesecondconceptisthatforeachcharacteranorganisminheritstwoalleles,onefromeachparentMendelmadethisdeductionwithoutknowingabouttheroleofchromosomesThetwoallelesatalocusonachromosomemaybeidentical,asinthetrue-breedingplantsofMendel’sPgenerationAlternatively,thetwoallelesatalocusmaydiffer,asintheF1hybrids

Copyright?2008PearsonEducationInc.,publishingasPearsonBenjaminCummingsThethirdconceptisthatifthetwoallelesatalocusdiffer,thenone(thedominantallele)determinestheorganism’sappearance,andtheother(therecessiveallele)hasnonoticeableeffectonappearanceIntheflower-colorexample,theF1plantshadpurpleflowersbecausethealleleforthattraitisdominant顯性性狀表現(xiàn)隱性性狀不表現(xiàn)Copyright?2008PearsonEducationInc.,publishingasPearsonBenjaminCummingsThefourthconcept,nowknownasthelawofsegregation,statesthatthetwoallelesforaheritablecharacterseparate(segregate)duringgameteformationandendupindifferentgametesThus,aneggoraspermgetsonlyoneofthetwoallelesthatarepresentinthesomaticcellsofanorganismThissegregationofallelescorrespondstothedistributionofhomologouschromosomestodifferentgametesinmeiosisCopyright?2008PearsonEducationInc.,publishingasPearsonBenjaminCummingsMendel’ssegregationmodelaccountsforthe3:1ratioheobservedintheF2generationofhisnumerouscrossesThepossiblecombinationsofspermandeggcanbeshownusingaPunnettsquare,adiagramforpredictingtheresultsofageneticcrossbetweenindividualsofknowngeneticmakeupAcapitalletterrepresentsadominantallele,andalowercaseletterrepresentsarecessivealleleCopyright?2008PearsonEducationInc.,publishingasPearsonBenjaminCummingsFig.14-5-1PGenerationAppearance:Geneticmakeup:Gametes:PurpleflowersWhiteflowersPPPpppFig.14-5-2PGenerationAppearance:Geneticmakeup:Gametes:PurpleflowersWhiteflowersPPPpppF1GenerationGametes:Geneticmakeup:Appearance:PurpleflowersPpPp1/21/2Fig.14-5-3PGenerationAppearance:Geneticmakeup:Gametes:PurpleflowersWhiteflowersPPPpppF1GenerationGametes:Geneticmakeup:Appearance:PurpleflowersPpPp1/21/2F2GenerationSpermEggsPPPPPpppPppp31UsefulGeneticVocabularyAnorganismwithtwoidenticalallelesforacharacterissaidtobehomozygous

forthegenecontrollingthatcharacter同質(zhì)基因Anorganismthathastwodifferentallelesforageneissaidtobeheterozygous

forthegenecontrollingthatcharacter異質(zhì)基因Unlikehomozygotes,heterozygotesarenottrue-breedingCopyright?2008PearsonEducationInc.,publishingasPearsonBenjaminCummingsBecauseofthedifferenteffectsofdominantandrecessivealleles,anorganism’straitsdonotalwaysrevealitsgeneticcompositionTherefore,wedistinguishbetweenanorganism’sphenotype表型,orphysicalappearance,anditsgenotype基因型,orgeneticmakeupIntheexampleofflowercolorinpeaplants,PPandPpplantshavethesamephenotype(purple)butdifferentgenotypesCopyright?2008PearsonEducationInc.,publishingasPearsonBenjaminCummingsFig.14-6PhenotypePurplePurple3PurpleGenotype1WhiteRatio3:1(homozygous)(homozygous)(heterozygous)(heterozygous)PPPpPpppRatio1:2:1112TheTestcross試交Howcanwetellthegenotypeofanindividualwiththedominantphenotype?Suchanindividualmusthaveonedominantallele,buttheindividualcouldbeeitherhomozygousdominantorheterozygousTheansweristocarryoutatestcross:breedingthe

mysteryindividualwithahomozygousrecessiveindividualIfanyoffspringdisplaytherecessivephenotype,themysteryparentmustbeheterozygousCopyright?2008PearsonEducationInc.,publishingasPearsonBenjaminCummingsFig.14-7TECHNIQUERESULTSDominantphenotype,unknowngenotype:PPorPp?PredictionsRecessivephenotype,knowngenotype:pp

IfPPIfPporSpermSpermppppPPPpEggsEggsPpPpPpPpPpPppppporAlloffspringpurple1/2offspringpurpleand1/2offspringwhiteFig.14-7aDominantphenotype,unknowngenotype:PPorPp?PredictionsRecessivephenotype,knowngenotype:pp

IfPPIfPporSpermSpermppppPPPpEggsEggsPpPpPpPpPpPpppppTECHNIQUEFig.14-7bRESULTSAlloffspringpurpleor1/2offspringpurpleand1/2offspringwhiteTheLawofIndependentAssortment獨立分配率MendelderivedthelawofsegregationbyfollowingasinglecharacterTheF1offspringproducedinthiscrossweremonohybrids,individualsthatareheterozygousforonecharacterAcrossbetweensuchheterozygotesiscalledamonohybridcrossCopyright?2008PearsonEducationInc.,publishingasPearsonBenjaminCummingsMendelidentifiedhissecondlawofinheritancebyfollowingtwocharactersatthesametimeCrossingtwotrue-breedingparentsdifferingintwocharactersproducesdihybrids

intheF1generation,heterozygousforbothcharactersAdihybridcross,acrossbetweenF1

dihybrids,candeterminewhethertwocharactersaretransmittedtooffspringasapackageorindependentlyCopyright?2008PearsonEducationInc.,publishingasPearsonBenjaminCummingsFig.14-8EXPERIMENTRESULTSPGenerationF1GenerationPredictionsGametesHypothesisofdependentassortmentYYRRyyrrYRyrYyRr

HypothesisofindependentassortmentorPredictedoffspringofF2generationSpermSpermYRYRyryrYrYRyRYryRyrYRYYRRYYRRYyRrYyRrYyRrYyRrYyRrYyRrYYRrYYRrYyRRYyRRYYrrYyrrYyrryyRRyyRryyRryyrryyrrPhenotypicratio3:1EggsEggsPhenotypicratio9:3:3:11/21/21/21/21/4yr1/41/41/41/41/41/41/41/43/49/163/163/161/16Phenotypicratioapproximately9:3:3:131510810132Fig.14-8aEXPERIMENTPGenerationF1GenerationPredictionsGametesHypothesisofdependentassortmentYYRRyyrrYRyrYyRr

HypothesisofindependentassortmentorPredictedoffspringofF2generationSpermSpermYRYRyryrYrYRyRYryRyrYRYYRRYYRRYyRrYyRrYyRrYyRrYyRrYyRrYYRrYYRrYyRRYyRRYYrrYyrrYyrryyRRyyRryyRryyrryyrrPhenotypicratio3:1EggsEggsPhenotypicratio9:3:3:11/21/21/21/21/4yr1/41/41/41/41/41/41/41/43/49/163/163/161/16Fig.14-8bRESULTSPhenotypicratioapproximately9:3:3:131510810132Usingadihybridcross,MendeldevelopedthelawofindependentassortmentThelawofindependentassortmentstatesthateachpairofallelessegregatesindependentlyofeachotherpairofallelesduringgameteformationStrictlyspeaking,thislawappliesonlytogenesondifferent,nonhomologouschromosomesGeneslocatedneareachotheronthesamechromosometendtobeinheritedtogetherCopyright?2008PearsonEducationInc.,publishingasPearsonBenjaminCummingsConcept14.2:ThelawsofprobabilitygovernMendelianinheritanceMendel’slawsofsegregationandindependentassortmentreflecttherulesofprobabilityWhentossingacoin,theoutcomeofonetosshasnoimpactontheoutcomeofthenexttossInthesameway,theallelesofonegenesegregateintogametesindependentlyofanothergene’sallelesCopyright?2008PearsonEducationInc.,publishingasPearsonBenjaminCummingsThemultiplicationrulestatesthattheprobabilitythattwoormoreindependenteventswilloccurtogetheristheproductoftheirindividualprobabilitiesProbabilityinanF1monohybridcrosscanbedeterminedusingthemultiplicationruleSegregationinaheterozygousplantislikeflippingacoin:EachgametehasachanceofcarryingthedominantalleleandachanceofcarryingtherecessivealleleTheMultiplicationandAdditionRulesAppliedtoMonohybridCrosses加乘法則Copyright?2008PearsonEducationInc.,publishingasPearsonBenjaminCummingsFig.14-9RrRr

SegregationofallelesintoeggsSpermRRRRRRrrrrrr1/21/21/21/2SegregationofallelesintospermEggs1/41/41/41/4TheruleofadditionstatesthattheprobabilitythatanyoneoftwoormoreexclusiveeventswilloccuriscalculatedbyaddingtogethertheirindividualprobabilitiesTheruleofadditioncanbeusedtofigureouttheprobabilitythatanF2plantfromamonohybridcrosswillbeheterozygousratherthanhomozygousCopyright?2008PearsonEducationInc.,publishingasPearsonBenjaminCummingsSolvingComplexGeneticsProblemswiththeRulesofProbabilityWecanapplythemultiplicationandadditionrulestopredicttheoutcomeofcrossesinvolvingmultiplecharactersAdihybridorothermulticharactercrossisequivalenttotwoormoreindependentmonohybridcrossesoccurringsimultaneouslyIncalculatingthechancesforvariousgenotypes,eachcharacterisconsideredseparately,andthentheindividualprobabilitiesaremultipliedtogetherCopyright?2008PearsonEducationInc.,publishingasPearsonBenjaminCummingsFig.14-UN1Concept14.3:InheritancepatternsareoftenmorecomplexthanpredictedbysimpleMendeliangeneticsTherelationshipbetweengenotypeandphenotypeisrarelyassimpleasinthepeaplantcharactersMendelstudiedManyheritablecharactersarenotdeterminedbyonlyonegenewithtwoallelesHowever,thebasicprinciplesofsegregationandindependentassortmentapplyeventomorecomplexpatternsofinheritanceCopyright?2008PearsonEducationInc.,publishingasPearsonBenjaminCummingsExtendingMendelianGeneticsforaSingleGeneInheritanceofcharactersbyasinglegenemaydeviatefromsimpleMendelianpatternsinthefollowingsituations:WhenallelesarenotcompletelydominantorrecessiveWhenagenehasmorethantwoallelesWhenageneproducesmultiplephenotypesCopyright?2008PearsonEducationInc.,publishingasPearsonBenjaminCummingsDegreesofDominanceCompletedominanceoccurswhenphenotypesoftheheterozygoteanddominanthomozygoteareidenticalInincompletedominance,thephenotypeofF1hybridsissomewherebetweenthephenotypesofthetwoparentalvarietiesIncodominance,twodominantallelesaffectthephenotypeinseparate,distinguishablewaysCopyright?2008PearsonEducationInc.,publishingasPearsonBenjaminCummingsFig.14-10-1RedPGenerationGametesWhiteCRCRCWCWCRCWFig.14-10-2RedPGenerationGametesWhiteCRCRCWCWCRCWF1GenerationPinkCRCWCRCWGametes1/21/2Fig.14-10-3RedPGenerationGametesWhiteCRCRCWCWCRCWF1GenerationPinkCRCWCRCWGametes1/21/2F2GenerationSpermEggsCRCRCWCWCRCRCRCWCRCWCWCW1/21/21/21/2Adominantalleledoesnotsubduearecessiveallele;allelesdon’tinteractAllelesaresimplyvariationsinagene’snucleotidesequenceForanycharacter,dominance/recessivenessrelationshipsofallelesdependonthelevelatwhichweexaminethephenotypeCopyright?2008PearsonEducationInc.,publishingasPearsonBenjaminCummingsTheRelationBetweenDominanceandPhenotypeTay-Sachs

diseaseisfatal;adysfunctionalenzymecausesanaccumulationoflipidsinthebrainAttheorganismallevel,thealleleisrecessiveAtthebiochemicallevel,thephenotype(i.e.,theenzymeactivitylevel)isincompletelydominantAtthemolecularlevel,theallelesarecodominantCopyright?2008PearsonEducationInc.,publishingasPearsonBenjaminCummingsFrequencyofDominantAllelesDominantallelesarenotnecessarilymorecommoninpopulationsthanrecessiveallelesForexample,onebabyoutof400intheUnitedStatesisbornwithextrafingersortoesCopyright?2008PearsonEducationInc.,publishingasPearsonBenjaminCummingsThealleleforthisunusualtraitisdominanttothealleleforthemorecommontraitoffivedigitsperappendageInthisexample,therecessivealleleisfarmoreprevalentthanthepopulation’sdominantalleleCopyright?2008PearsonEducationInc.,publishingasPearsonBenjaminCummingsMultipleAllelesMostgenesexistinpopulationsinmorethantwoallelicformsForexample,thefourphenotypesoftheABObloodgroupinhumansaredeterminedbythreeallelesfortheenzyme(I)thatattachesAorBcarbohydratestoredbloodcells:IA,IB,andi.TheenzymeencodedbytheIAalleleaddstheAcarbohydrate,whereastheenzymeencodedbytheIBalleleaddstheBcarbohydrate;theenzymeencodedbytheialleleaddsneitherCopyright?2008PearsonEducationInc.,publishingasPearsonBenjaminCummingsFig.14-11IAIBiABnone(a)ThethreeallelesfortheABObloodgroupsandtheirassociatedcarbohydratesAlleleCarbohydrateGenotypeRedbloodcellappearancePhenotype(bloodgroup)IAIAorIAiABIBIBorIBiIAIBABiiO(b)BloodgroupgenotypesandphenotypesPleiotropyMostgeneshavemultiplephenotypiceffects,apropertycalledpleiotropyForexample,pleiotropicallelesareresponsibleforthemultiplesymptomsofcertainhereditarydiseases,suchascysticfibrosisandsickle-celldiseaseCopyright?2008PearsonEducationInc.,publishingasPearsonBenjaminCummingsExtendingMendelianGeneticsforTwoorMoreGenesSometraitsmaybedeterminedbytwoormoregenesCopyright?2008PearsonEducationInc.,publishingasPearsonBenjaminCummingsEpistasisInepistasis,ageneatonelocusaltersthephenotypicexpressionofageneatasecondlocusForexample,inmiceandmanyothermammals,coatcolordependsontwogenesOnegenedeterminesthepigmentcolor(withallelesBforblackandbforbrown)Theothergene(withallelesCforcolorandcfornocolor)determineswhetherthepigmentwillbedepositedinthehairCopyright?2008PearsonEducationInc.,publishingasPearsonBenjaminCummingsFig.14-12BbCcBbCcSpermEggsBCbCBcbcBCbCBcbcBBCC1/41/41/41/41/41/41/41/4BbCCBBCcBbCcBbCCbbCCBbCcbbCcBBCcBbCcBbCcbbCcBBccBbccBbccbbcc9:3:4

PolygenicInheritanceQuantitativecharactersarethosethatvaryinthepopulationalongacontinuumQuantitativevariationusuallyindicatespolygenicinheritance,anadditiveeffectoftwoormoregenesonasinglephenotypeSkincolorinhumansisanexampleofpolygenicinheritanceCopyright?2008PearsonEducationInc.,publishingasPearsonBenjaminCummingsFig.14-13EggsSpermPhenotypes:Numberofdark-skinalleles:01234561/646/6415/6420/6415/646/641/641/81/81/81/81/81/81/81/81/81/81/81/81/81/81/81/8AaBbCcAaBbCc

NatureandNurture:TheEnvironmentalImpactonPhenotypeAnotherdeparturefromMendeliangeneticsariseswhenthephenotypeforacharacterdependsonenvironmentaswellasgenotypeThenormofreactionisthephenotypicrangeofagenotypeinfluencedbytheenvironmentForexample,hydrangeaflowersofthesamegenotyperangefromblue-violettopink,dependingonsoilacidityCopyright?2008PearsonEducationInc.,publishingasPearsonBenjaminCummingsFig.14-14NormsofreactionaregenerallybroadestforpolygeniccharactersSuchcharactersarecalledmultifactorialbecausegeneticandenvironmentalfactorscollectivelyinfluencephenotypeCopyright?2008PearsonEducationInc.,publishingasPearsonBenjaminCummingsIntegratingaMendelianViewofHeredityandVariationAnorganism’sphenotypeincludesitsphysicalappearance,internalanatomy,physiology,andbehaviorAnorganism’sphenotypereflectsitsoverallgenotypeanduniqueenvironmentalhistoryCopyright?2008PearsonEducationInc.,publishingasPearsonBenjaminCummingsConcept14.4:ManyhumantraitsfollowMendelianpatternsofinheritanceHumansarenotgoodsubjectsforgeneticresearch

– Generationtimeistoolong

– Parentsproducerelativelyfewoffspring

– BreedingexperimentsareunacceptableHowever,basicMendeliangeneticsenduresasthefoundationofhumangeneticsCopyright?2008PearsonEducationInc.,publishingasPearsonBenjaminCummingsPedigreeAnalysisApedigreeisafamilytreethatdescribestheinterrelationshipsofparentsandchildrenacrossgenerationsInheritancepatternsofparticulartraitscanbetracedanddescribedusingpedigreesCopyright?2008PearsonEducationInc.,publishingasPearsonBenjaminCummingsFig.14-15KeyMaleFemaleAffectedmaleAffectedfemaleMatingOffspring,inbirthorder(first-bornonleft)1stgeneration(grandparents)2ndgeneration(parents,aunts,anduncles)3rdgeneration(twosisters)WwwwwwWwWwwwwwWwWwwwwwWwWWorWidow’speakNowidow’speak(a)Isawidow’speakadominantorrecessivetrait?1stgeneration(grandparents)2ndgeneration(parents,aunts,anduncles)3rdgeneration(twosisters)FfFfFfFfFfFfFForffffffffffFForFfAttachedearlobeFreeearlobe(b)Isanattachedearlobeadominantorrecessivetrait?Fig.14-15aKeyMaleFemaleAffectedmaleAffectedfemaleMatingOffspring,inbirthorder(first-bornonleft)Fig.14-15b1stgeneration(grandparents)2ndgeneration(parents,aunts,anduncles)3rdgeneration(twosisters)Widow’speakNowidow’speak(a)Isawidow’speakadominantorrecessivetrait?WwwwWwWwwwwwwwwwWwWwwwWWWworFig.14-15cAttachedearlobe1stgeneration(grandparents)2ndgeneration(parents,aunts,anduncles)3rdgeneration(twosisters)Freeearlobe(b)Isanattachedearlobeadominantorrecessivetrait?FfFfFfFfFfffFfffffffffFFororFFFfPedigreescanalsobeusedtomakepredictionsaboutfutureoffspringWecanusethemultiplicationandadditionrulestopredicttheprobabilityofspecificphenotypesCopyright?2008PearsonEducationInc.,publishingasPearsonBenjaminCummingsRecessivelyInheritedDisordersManygeneticdisordersareinheritedinarecessivemannerCopyright?2008PearsonEducationInc.,publishingasPearsonBenjaminCummingsTheBehaviorofRecessiveAllelesRecessivelyinheriteddisordersshowuponlyinindividualshomozygousforthealleleCarriersareheterozygousindividualswhocarrytherecessiveallelebutarephenotypicallynormal(i.e.,pigmented)AlbinismisarecessiveconditioncharacterizedbyalackofpigmentationinskinandhairCopyright?2008PearsonEducationInc.,publishingasPearsonBenjaminCummingsFig.14-16ParentsNormalNormalSpermEggsNormalNormal(carrier)Normal(carrier)AlbinoAaAaAAAAAaaAaaaa

Ifarecessiveallelethatcausesadiseaseisrare,thenthechanceoftwocarriersmeetingandmatingislowConsanguineousmatings(i.e.,matingsbetweencloserelatives)increasethechanceofmatingbetweentwocarriersofthesamerarealleleMostsocietiesandcultureshavelawsortaboosagainstmarriagesbetweencloserelativesCopyright?2008PearsonEducationInc.,publishingasPearsonBenjaminCummingsCysticFibrosisCysticfibrosisisthemostcommonlethalgeneticdiseaseintheUnitedStates,strikingoneoutofevery2,500peopleofEuropeandescentThecysticfibrosisalleleresultsindefectiveorabsentchloridetransportchannelsinplasmamembranesSymptomsincludemucusbuildupinsomeinternalorgansandabnormalabsorptionofnutrientsinthesmallintestineCopyright?2008PearsonEducationInc.,publishingasPearsonBenjaminCummingsSickle-CellDiseaseSickle-celldiseaseaffectsoneoutof400African-AmericansThediseaseiscausedbythesubstitutionofasingleaminoacidinthehemoglobinproteininredbloodcellsSymptomsincludephysicalweakness,pain,organdamage,andevenparalysisCopyright?2008PearsonEducationInc.,publishingasPearsonBenjaminCummingsDominantlyInheritedDisordersSomehumandisordersarecausedbydominantallelesDominantallelesthatcausealethaldiseasearerareandarisebymutationAchondroplasiaisaformofdwarfismcausedbyararedominantalleleCopyright?2008PearsonEducationInc.,publishingasPearsonBenjaminCummingsFig.14-17EggsParentsDwarfNormalNormalNormalDwarfDwarfSpermDd

dddDDdddddDdddHuntington’sdiseaseisadegenerativediseaseofthenervoussystemThediseasehasnoobviousphenotypiceffectsuntiltheindividualisabout35to40yearsofageHuntington’sDiseaseCopyright?2008PearsonEducationInc.,publishingasPearsonBenjaminCummingsMultifactorialDisordersManydiseases,suchasheartdiseaseandcancer,havebothgeneticandenvironmentalcomponentsLittleisunderstoodaboutthegeneticcontributiontomostmultifactorialdiseasesCopyright?2008PearsonEducationInc.,publishingasPearsonBenjaminCummingsGeneticTestingandCounselingGeneticcounselorscanprovideinformationtoprospectiveparentsconcernedaboutafamilyhistoryforaspecificdiseaseCopyright?2008PearsonEducationInc.,publishingasPearsonBenjaminCummingsCounselingBasedonMendelianGeneticsandProbabilityRulesUsingfamilyhistories,geneticcounselorshelpcouplesdeterminetheoddsthattheirchildrenwillhavegeneticdisordersCopyright?2008PearsonEducationInc.,publishingasPearsonBenjaminCummingsTestsforIdentifyingCarriersForagrowingnumberofdiseases,testsareavailablethatidentifycarriersandhelpdefinetheoddsmoreaccuratelyCopyright?2008PearsonEducationInc.,publishingasPearsonBenjaminCummingsFetalTestingInamniocentesis,theliquidthatbathesthefetusisremovedandtestedInchorionicvillussampling(CVS),asampleoftheplacentaisremovedandtestedOthertechniques,suchasultrasoundandfetoscopy,allowfetalhealthtobeassessedvisuallyinuteroCopyright?2008PearsonEducationInc.,publishingasPearsonBenjaminCummingsVideo:UltrasoundofHumanFetusIFig.14-18AmnioticfluidwithdrawnFetusPlacentaUterusCervixCentrifugationFluidFetalcell