Test Bank - for Essentials of Genetics 20th Edition by William Klug, All Chapters 1-21 Complete Guide A+.pdf

Test Bank For Human Genetics, 13th Edition All Chapters
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-



Lectureg1:g-gggANSWERgg

-gDNAgisgpackagedgasgchromatin,gchromosomesgbecomegvisiblegduringgmitosis.g-
gggANSWERgg




Homologues-g(maternalgandgpaternalgformsgofgsamegchromosome)g-gggANSWERgg

Meiosis:gG1,gS,gG2,gM.gBeforegreplicationgphase,gchromosomesghavegonegchromatidga
ndgaftergreplication,gchromosomesghaveg2gsistergchromatids,gheldgtogethergatgthegcentr
omere.gEndsgwithg4gdaughtergcellsgwithg1gchromatidgeach.g-gggANSWERgg

Keygdifferencesgfromgmitosis:gHomologsgpairg(ProphasegI),gSistergcentromeresgactgasga
gsinglegcentromereg(MetaphasegI),gSistergchromatidsgremaingattachedg(AnaphasegI),gM

eiosisgIgisgagreductiongdivision-
gmeaninggstartgmeiosisgIgwithg46gunitsgandgendgmeiosisgIgwithg23gunitsg(g2gchromatidsging

eachghaploidgdaughtergcells),gMeiosisgIIgisgangequationalgdivisiong(identicalgtogmitosis).g-
gggANSWERgg




RecombinationgoccursgingProphasegI.gCrossinggovergandgrecombgisgExchangegofghomo
logousgsegmentsgbetweengnon-sistergchromatids.g-gggANSWERgg

HomologuesgmovegapartgduringganaphasegI-
disjunction.g223gpossiblegcombinationsgofgchromosomes.gIngcytokinesisgI,gCellsgdividegi
ntogtwoghaploidgdaughtergcells.gOnegcellgreceivesgmostgofgthegcytoplasmgandgthegotherg
becomesgthegfirstgpolargbodygwhichgdoesn'tggogthroughgMeiosisgII.gMeiosisgIgendsgafterg
ovulation.gNongdysjunctiongingmeiosisgI:gcangcausegproblemsglikegTrisomyg21.g-
gggANSWERgg




-
Briefginterphasegbetweengfirstgandgsecondgmeioticgdivisions.gNogSgphasegoccursgingMei
osisgII.g-gggANSWERgg

-
Ingthegsecondgmeioticgdivisiongagsecondgpolargbodygformsgduringgoogenesis.gIngoogene
sis,gegggisgarrestedgingmetaphasegIIguntilgfertilization.g-gggANSWERgg

AftergMeiosisgtheregisgagReductiongofgchromosomegnumberg2nn.g(diploidgvs.ghaploidgcel
ls)-
gNotationg'n'ghasgtogdogwithgamountgofgDNAg(#of gnucleotides),gnotgthegnecessarilygtheg#g

ofgchromosomes.g-gggANSWERgg

,Lectureg2:gPatternsgofgInheritanceg-gggANSWERgg

MedeliangInheritance-
gdeterminedgbygagsingle gmajorggene.gBasedgongindependentgassortment.gDihybridgcros

sg(2ggenotypes)gwithgry,gRy,grY,gRygsetgupgongbothgsidesphenotypicgratiogofg9:3:3:1-
yellowground,ggreenground,gyellowgwrinkled,ggreengwrinkled,gIfggetg9:3:3:1gyougknowgtha
tgsegregationgisgindependent.g-gggANSWERgg

Multifactorialginheritance-multipleggeneticgandgnon-geneticgfactorsginvolvedg-
gggANSWERgg




Compoundgheterozygous:ghasgtwogdifferentgmutantgallelesgforgagcharacterg-
gggANSWERgg




Linkage-
2ggenesgphysicallygneargeachgothergongagchromosomegwillgnotgassortgrandomlygingmeio
sis.gTightlyglinked:gwillggetg2gtypesgofggametesgex.gPLgandgpl.gUnlinked:gwillggetg4gtypesg
ofggametesgPL,gPl,gpL,gpl.g-gggANSWERgg

Thegfrequencygofgrecombinationgbetweengtwoggenesgisgproportionalgtogthegdistancegbet
weengtheggenes.gThegclosergtheggenesgaregongthegchromosomegtheglessglikelygcrossingg
overgoccurs.gLinkagegmap:g1%grecombinationg=g1gmapgunitg=g1gcentiMorgang(cM),gMap
gdistancesgaregadditive.g-gggANSWERgg




Thegnon-
randomgassociationgbetweengallelesgatgtwoglocationsgongagchromosomegisgcalledglinkag
egdisequilibrium.gIfgthegfrequencygofgchromosomesgwithgAB=Ab=aB=abgthengtheggenes
garegingequilibrium.gIfgfrequencygofg1gallelegisgseengmoreg(AgmoregthangBgforgex)gthengge

nesgareginglinkagegdisequilibrium.g-gggANSWERgg

AutosomalgdominantginheritancegExamples:g-gggANSWERgg

Achondroplasia-
gFGFR3gmutations,gAlwaysgfullgpenetrancegwithgachondroplasiag(sognormalgparentsgha

vegagchildgwithgaplasiagthengit'sgagnewgmutation).gHeterozygousgb/cghomozygotesgusual
lygdieginguterog-gggANSWERgg

Neurofibromatosis-gNF1g(neurofibromin)gandgNF2g(merlin)gmutations.g-gggANSWERgg

Incompletegdominance-
gmixedgphenotype.gIngcasesgofgdisease,gDominantgdisordersgaregmoregsevereginghomoz

ygotesgthengingheterozygotesg(termedgalsog"semidominant")gIe.gFamilialgHypercholeste
rolemia.g-gggANSWERgg

Co-dominance-
gphenotypicgexpressiongofgtwogdifferentgallelesgforgaglocusgie.gBloodgtype.g-gggANSWERgg




Autosomalgrecessiveginheritance:gExamples:gCysticgfibrosis,gTay-
Sachsgdisease,gSickle-cellgdiseaseg-gggANSWERgg

,Pseudodominance:gtheginheritancegofgangautosomalgrecessivegtraitgmimicsgangautoso
malgdominantgpatterng-gggANSWERgg

MalesgareghemizygousgwithgrespectgtogX-linkedggenes.g-gggANSWERgg

X-
linkedgdominantginheritance:gAffectedgfemalesgaregtwicegasgcommongasgaffectedgmales
gbutgmalesgusuallygmoregseverelygaffectedgorgthegdisordergmaygbeglethalgingmalesg(Rettg

syndrome).g-gggANSWERgg

X-
linkedgrecessive:gincidencegisgmuchghighergingmalesgandgaffectedgmalesgdognotgusuallyg
transmitgthegdisordergunlessgmothergisgagcarrier.gHeterozygotegfemalesgaregusuallyguna
ffected,gbutgsomegmaygexpressgthegconditiongwithgvariablegseveritygasgdeterminedgbygth
egpatterngofgXginactivation.gAgsignificantgproportiongofgisolatedgcasesgaregduegtognewgmu
tationg(Duchennegmusculargdystrophy-DMD).g-gggANSWERgg

Pseudoautosomalginheritance-
ggroupgofggenesgongtheginactivegxgchromosomegaregNOTginactivated.gDiseasesgassocia

tedgwithgtheseggenesgareginheritedgsimilargtogautosomalginheritance.g-gggANSWERgg

SamegamountgofgX-
linkedggenegproductsgbetweengmalesgandgfemalesgachievedgthroughgdosagegcompens
ation.gLyongHypothesisgstatesgthatgtheginactivegXgisgNOTgrandomlygchosengingeachgcellg
Ex.gAgstructurallygabnormalgXgisgpreferentiallyginactivated.gInactivationgisgNOTgcomplet
e-
gsomeggenesgcangescapeginactivationg(ie.gThosegwithgagfunctionalghomologgongthegY).gI

nactivationgisgNOTgpermanent-
greversedgingdevelopmentgofggermgcellsg(notgpassedgongtoggametes).g-gggANSWERgg




ThegkeygplayergisgthegX-
linkedggenegXIST→gXg(inactive)gspecificgtranscript.gXISTgisgtranscribedgtogproducegagno
n-codinggRNAgthatg"coats"gthegX-
chromosomegandginactivatesgit.gXISTgisgonlygexpressedgfromgtheginactivegX.gTheghiston
esgongthegcoatedgXgundergogmethylationgwhichgcausesgthegchromosomegtogcondenseg(
heterochromatin),gforminggagBarrgbody.g-gggANSWERgg

-
SomeggenesgdognotghavegYghomologuegandgdognotgundergoginactivationg(e.g.gsteroidgs
ulfataseggene)g-gggANSWERgg

-Random/skewedginactivationgmaygresultgingaffected/totallyghealthygheterozygotes.g-
gggANSWERgg




VariablegexpressiongofgX-
inactivation:gOngbothgextremes,gagheterozygousgfemalegwithgrecessivegx-
linkedgdiseasegcouldgmanifestgthegdisease.gIngagcasegwithgagdominantgX-
linkedgtrait,gingwhichgalmostgallgofgagfemalesgXgchromosomesgwithgmutationgisginactive,g
mightgnotgmanifestgthisgdisease.gIdenticalgtwinsgcouldgevenghavegdiffgphenotypesgduegt
ogskewedgXginactivation.g-gggANSWERgg

, Mosaicism-
gXgchromosomeginactivationgoccursgrandomlygandginactivationgpatterngisgpassedgtogcellg

progeny.gResult:gfunctionalgmosaicismgingwhichgfemalegisgagmosaicgwithgrespectgtogexp
ressiongofggenesgongXgchrom.gEx.gCalicogCat,gBg-gdominantgorange,gbg-
grecessiveggenegblack,gGenesgforgwhite:gautosomal.g-gggANSWERgg




GeneticgHeterogeneitygcangbegthegresultgofgLocusgHeterogeneityg,gAllelicgHeterogeneit
y,gandgModifiergLoci.g-gggANSWERgg

LocusgHeterogeneity-
gagsinglegdisorder,gtrait,gorgpatterngofgtraitsgcausedgbygmutationsginggenesgatgdifferentgch

romosomalgloci.gEx.gretinitisgpigmentosaghasgautosomalgdominant,gautosomalgrecessiv
e,gandgX-
linkedgorigins.gHowever,gonlygonegmutantglocusgisgneededgforgthegphenotypegtogmanifes
tg-gggANSWERgg

Allelicgheterogeneityg-
gManyggeneticglocigpossessgmoregthangonegmutantgallele.gIngthegCFTRggene,gnearlyg14

00gmutationsgfound.gSomegmutationsgcausegclassicalgCFg+gpancreaticginsufficiencyg+gc
ongenitalgabsencegofgvasgdeferens,gothersgcauseglunggdiseasegwithgnormalgpancreaticg
fxn.gOthergcausegonlygmalegsterility.g-gggANSWERgg

Modifierggene:gAggenegthatgaffectsgthegphenotypicgexpressiongofganotherggene.gSpecifi
cgallelesgofgonegorgmoreggenesg(modifierggenes)gcangsometimesgdramaticallygmodifygth
egclinicalgseveritygofgthegphenotypegproducedgbygmutationsgingagdisease-
causingggene.Thisgsourcegofgclinicalgheterogeneitygisgoftengreferredgtogasggeneticgback
ground.gEx.gTwinsgwithgthegsamegmutationgingcysticgfibrosisgbutgonegisgseverelygsickgan
dgonegonlygmoderatelygsick-gexplainedgbygmodifierggenes.g-gggANSWERgg

CandidateglocigactinggasgmodifiersgforgCFTRgmutations:TGFB1g(cytokinegtransformingg
growthgfactorgbgandgMLB2g(Mannose-
bindingglectin).gDifferentgallelesgofgtheseggenesgmodifygthegseveritygofgCFg-gggANSWERgg

Clinical/phenotypicgheterogeneity:gmultiplegphenotypesgofgonegsingleggenegex.gUSH2A
ggene,gcodesgforgproteingimportantgingdevelopmentgofgtheginnergeargandgretina.gCangbeg

blindgandgdeafg(typegIIgUshergsyndrome)gorgjustgblindg(RetinitisgPigmentosa).g-
gggANSWERgg




Othergfactorsgaffectiongphenotypegincludegenvironmentalgfactorsgie.gG6PDgmutationgO
RgsoilgpHgandghydrangeagcolor.gAlsogSex-
relatedgfactorsgiegHemochromatosis,gAR,gcausedgbygirongoverload,gisglessgcommongingf
emalesgduegtoglowergirongintake/menstrualgirongloss.g-gggANSWERgg

G6PDg(glucose-6-phosphategdehydrogenase)gDeficiencyg(X-linked)-
gCangleadgtoghemolyticganemia,gmanygpplgwithgthisgdisordergnevergexperienceganygsym

ptoms.gHemolyticganemiagcangbegtriggeredgbygenvironmentalgfactorsgsuchgasgbacterial/
viralginfections,gdrugg(sulfa,gmalariagmedications),geatinggfavagbeansgorginhalinggfavagb
eangplantgpollen.g-gggANSWERgg