遗传学双语课练习题资料.docx

遗传学双语课练习题资料.docx

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遗传学双语课练习题资料

Medialiangenetics

1ShownareF2resultsoftwoofMendel'smonohybridcrosses.Stateanullhypothesisthatyouwilltestusingchi-squareanalysis.Calculatethex2valueanddeterminethepvalueforbothcrosses,theninterpretthepvalues.Whichcrossshowsagreateramountofdeviation?

（a）Fullpods882

Constrictedpods299

（b）Violetflowers705

Whiteflowers224

2InDmsophihla,gaybodycolorisdominantoverebonybodycolor,whilelongwingsaredominantovervestigialwings.WorkthefollowingcrossesthroughtheeF2generation,anddeterminethegenotypicandphenotypicratiosforeachgeneration.AssumethatthePlindividualsarehomozygous:

（a）gray,long×ebony,vestigial（b）gray,vestigial×ebony,long（c）gray,long×gray,vestigial

3.Howmanydifferenttypesofgametescanbeformedbyindividualsofthefollowinggenotypes?

Whataretheyineachcase?

（a）AaBb,（b）AaBB,（c）AaBbCc,（d）AaBBcc,（e）AaBbccand（f）AaBbCcDdEe?

4.Usingtheforked-linemethod,detenninetheegenotypicandphenotypicratiosofthesetrihybridcrosses:

（a）AaBbCc×AaBBCC,（b）AaBBCc×aaBBCc,and（c）AaBbCc×AaBbCc.

5.Mendelcrossedpeaswithround,greenseedswithpeashavingwrinkled,yellowseeds.AllFlplantshadseedsthatwereroundandyellow-PredicttheresultsoftestcrossingtheseF1plants.

6.InoneofMendel'sdihybridcrosses,heobserved315round,yellow;108round,green;101wrinkled,yellow;and32wrinkled,greenF2plants.Analyzethesedatausingchi--squareanalysistoseewhether（a）theyfita9:

3:

3:

1ratio;（b）theround,wrinkledtraitfitfora3:

1ratio;or（c）theyellow,greentraitsfita3:

1ratio.

7.Ageneticist,inassessingdatathatfellintotwophenotypicclasses,observedvaluesof250:

150.Hedecidedtoperformchi-squareanalysisusingtwodifferentnullhypotheses:

（a）Thedatafita3:

1ratio;and（b）thedatafital:

1ratio.CalculatetheX2valuesforeachhypothesis-Whatcanyouconcludeabouteachhypothesis?

8.Thebasisforrejectinganynullhypothesisisarbitrary.Theresearchercansetmoreorlessstringentstandardsbydecidingtoraiseorlowerthecriticalpvalue.Wouldtheuseofastandardofp=0.10bemoreorlessstringentinfailingtorejectthenullhypothesis?

Explain.

9.Considerthreeindependentlyassortinggenepairs,A/a,B/b,andC/c,whereeachdemonstratestypicaldominance（A-,B-,C-）,andrecessiveness（aa,bb,cc）.WhatistheprobabilityofobtainingoffspringthatisAABbCcfromparentsthatareAaBbCCandAABbCc?

10.WhatistheprobabilityofobtainingatriplyrecessiveindividualfromtheeparentasshowninProblem9?

11.OfalloffspringoftheParentsinProblem9,whatproportionwillexpressallthreedominanttraits?

12.Forthefollowingpedigree,predictthemodeofinheritanceandtheresultinggenotypesofeachindividual.AssumethattheallelesAandacontroltheexpressionofthetrait.

13.WhichofMendel'spostulatesaredemonstratedbythepedigreeinProblem12?

Listanddefinethesepostulates.

14.Thefollowingpedigreefollowstheinheritanceofmyopia（near-sightedness）inhumans.Predictwhetherthedisorderisidentifiedasadominantorarecessivetrait.Basedonyourpredic6on,indicatethemostprobablegenotypeforeachindividual.

15.Twotrue-breedingpeaplantsarecrossed.Oneparentisround,terminal,violet,constricted,whiletheotherexpressesthecontrastingphenotypesofwdnkled,axial,white,full.Thefourpairsofcontrastingtraitsarecontrolledbyfourgenes,eachlocatedonaseparatechromosome.IntheF1generationonlyround,axial,violet,andfullareexpressed.IntheF2generation,allpossiblecombinationsofthesetraitsareexpressedinratiosconsistentwithMendelianinheritance.

（a）WhatconclusioncanyoudrawabouttheinheritanceofthesetraitsbasedontheFlresults?

（b）WhichphenotypeappearsmostfrequentlyintheF2results?

Writeamathematicalexpressionthatpredictsthefrequencyofoccurrenceofthisphenotype.

（c）WhichF2phenotypeisexpectedtooccur1eastfrequently?

Writeamathematicalexpressionthatpredictsthisfrequency.

（d）HowofteniseitherPlphenotypelikelytooccurintheF2generation?

（e）IftheFlplantistestcrossed,howmanydifferentphenotypeswillbeproduced,andhowdoesthisnumbercomparetothenumberofdifferentphenotypesintheF2generationdiscussedinpart（b）?

16.Tay-Sachsdisease（TSD）isaninbornerrorofmetabolismthatresultsindeath,usual1ybeforetheageoffive.Youareageneticcounselor,andyouinterviewaphenotypicallynormalcouplewhoconsultyoubecausethemanhadafemalefirstcousin（onMsfather'sside）whodiedtomTSD,andthewomanhadamaternalunclewithTSD.Therearenootherknowncasesineitherfamily,andnoneofthematingswere/arebetweenrelatedindividuals.Assumethatthistraitisrareinthispopulation.

（a）Usingstandardpedigreesymbols,drawapedigreeoftheseindividuals,families,showingtherelevantindividuals.

（b）ThecoupleasksyoutocalculatetheprobabilitythattheybothareheterozygousfortheTSDallele.

（c）Theyalsowanttoknowtheprobabilitythatneitherofthemisheterozygous.

（d）Theyalsoaskyoufortheprobabilitythatoneofthemisheterozygousbuttheotherisnot.

[Hint:

theeanswersto（b）,（c）,and（d）shouldaddupto1.0.]

17Chlamydomonas,aeukaryoticgreenalga,issensitivetotheantibioticerythromycin,whichinhibitsproteinsynthesisinprokaryotes.Therearetwomatingtypesinthisalga,mt+andmt-,Ifanmt+cellsensitivetotheantibioticiscrossedwithanmt-cellthatisresistant,allprogenycellsaresensitive.Thereciprocalcross（mt+resistantandmt-sensitive）yieldsallresistantprogenycells.AssumingthatthemutationforresistanceisinthechloroplastDNA,whatcanyouconcludefromtheresultsfromthesecrosses?

sexdetermination

1.Asrelatedtosexdetermination,whatismeantby（a）homomorphicandheteromorphicchromosomes;（b）isogamousandheterogamousorganisms?

2.ContrastthelifecycleofaplantsuchaszeamayswithananimalsuchasC.elegans-.

3.Discusstheroleofsexualdifferentiationinthelifecyclesofchlamydomonas,ZEmays,andC.elegans.

4.Distinguishbetweentheconceptsofsexualdifferentiationandsexdetem1ination.

5.ContrasttheProtenorandLygaeusmodesofsexdetermination.

6.DescribethemajordifferencebetweensexdeterminationinDrosophilaandinhumans.

7.Whatspecificobservations（evidence）supporttheconclusionsyouhavedrawnaboutsexdeterminationinDrosophilaandhumans?

8.DescribehownondisjunctioninhumanfemalegametescangiverisetoKlinefelterandTurnersyndromeoffspringfollowingfertilizationbyanormalmalegamete.

9.Aninsectspeciesisdiscoveredinwhichtheheterogameticsexisunknown.AnX-linkedrecessivemutationforreducedwing（rw）isdiscovered.ContrasttheF1andF2generationsfromacrossbetweenafemalewithreducedwingsandamalewithnormalsizedwingswhen（a）thefemaleistheheterogameticsex;（b）themaleistheheterogameticsex.

10.Basedonyouranswersinboblem9,isitpossibletodistinguishbetweenProtenorandLygaeusmodeofsexdeterminationbasedontheoutcomeofthesecrosses?

11.WhenCOWShavetwincalvesofunlikesex（fraternaltwins）,thefemaletwinisusuallysterileandhasmasculinindreproductiveorgans.Thiscalfisreferredtoasafreemartin.Incows,twinsmayshareacommonplacentaandthusfetalcirculation.Predictwhyafreemartindevelops.

12.Ithasbeensuggestedthatanymale-determininggenescontainedontheYchromosomeinhumanscannotbelocatedinthelimitedregionthatsynapseswiththeXchromosomeduringmeiosis.Whatmightbetheoutcomeifsuchgeneswerelocatedinthisregion?

13.WhatisaBarrbody,andwhereisitfoundinacell?

14.IndicatetheexpectednumberofBarrbodiesininterphasecellofthefollowingindividuals;KIinefeltersyndrome;Tumersyndrome;andkaryotypes47,XYY,47,XXX,and48,XXXX.

15.DefinetheLyonhypothesis.

16.CantheLyonhypothesisbetestedinahumanfemalewhoishomozygousforonealleleoftheX-linkedG6PDgene?

Why,orwhynot?

17.PredictthepotentialeffectoftheLyonhypothesisontheregionofahumanfemaleheterozygousfortheX-linkedred-greencolorblindnesstrait.

18.CatbreedersareawarethatkittensexpressingtheX-linkedcalicocoatpatternandtortoiseshellpatternarealmostinvariablefemales.Why?

19.Whatdoestheapparentneedfordosagecompensationmechanismssuggestabouttheexpressionofgeneticinformationinnormaldiploidindividuals?

LinkageandChromosomeMappingineukaryotyes

1.Whatisthesignificanceofcrossingover（whichleadstogeneticrecombinationtotheprocessofevolution?

2.Describethecytologicalobservationthatsuggeststhatcrossingoveroccursduringthefirstmeioticprophase.

3.Whydoesmorecrossingoveroccurbetweentwodistantlylinkedgenesthanbetweentwogenesthatareeveryclosetogetheronthesamechromosome?

4.Whyisa50percentrecoveryofsingle-crossoverproductstheupperlimit,evenwhencrossingoveralwaysoccursbetweentwolinkedgenes?

5.Whyaredouble-crossovereventsexpectedlessfrequentlythansingle-crossoverevents?

6.Whatistheproposedbasisforpositiveinterference?

7.Whatthreeessentialcriteriamustbemetinordertoexecuteasuccessfulmappingcross?

8.Thegenesdumpywings（dp）,cloteyes（cl）,andapterouswings（ap）arelinkedonchromosomeIIofDrosophilia.inaseriesoftwo-pointmappingcrosses,thegeneticdistancesshownbelowweredetermined-Whatisthesequenceofthethreegenes?

dp-ap42dp-cl3ap-cl39

9.Considertwohypotheticalrecessiveautosomalgenesaandb,whereaheterozygoteis