GeneticsWord文档格式.docx

GeneticsWord文档格式.docx

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Parentalgenotypes

Offspring

Genotype

Frequency

I

AbBb×

aabb

AaBb

aaBb

Aabb

25%

II

CcDd×

ccdd

CcDd

ccDd

Ccdd

46%

3%

4%

47%

（i）BrieflydiscussthegeneticprincipledemonstratedinCrossI,andsuggesthowsuchgenotypicfrequenciesintheoffspringareobtained.（3marks）

（ii）Withreferencetothelocationoftherespectivegenesonthechromosomes,explainthedifferencesinthegenotypicfrequencyoftheoffspringinCrossesIandII（5marks）

SuggestedSolution…

HKALE1991BiologyPaperII

1.（a）Explainthemeaningofthefollowingterms

（i）allele

（ii）polyploidy

（iii）hybridvigour（6marks）

（b）Inacertainspeciesofbird,onegenelocuscontrolsgeneralfeathercolour,withgreenbeingdominanttoblue.Asecondlocuscontrolscolourintensityandtheallelesatthislocusshowincompletedominance.Thetablebelowshowsthesixpossiblephenotypes:

Feathercolour

Colourintensity

Pale

Mid

Dark

　Green

palegreen

deepgreen

brownishgreen

　Blue

paleblue

deepblue

purple

（i）Drawgeneticdiagramstoillustratethefollowingcrosses:

（1）Homozygousdeepgreenxheterozygousbrownishgreen

（2）Homozygouspalegreenxdeepblue

Includeinyourdiagrams,thegenotypesoftheparents,zygotesandoffspring,

thephenotypesoftheoffspring,andthephenotyperatio.Defineallthesymbolsyouuse.

（10marks）

（ii）Describetheeasiestwaytodeterminewhetheradeepgreenindividualishomozygousorheterozygous.Explainyouranswer.（4marks）

HKALE1992BiologyPaperII

4.（a）Explainbymeansofageneticdiagramhowafemalechildcouldinherithaemophilia.（8marks）

（b）Explainwhyitisrareforahaemophiliacfemaletosurvivebeyondtheageofpuberty.（3marks）

（c）Whatadvicewouldyougivetothemotherofthechildinpart（a）ifshewerepregnantwithasecondfemalefoetus?

Givereasonsforyouradvice.（3marks）

（d）Givetwowaysbywhichmutationsmayoccurin

（i）genes.

（ii）chromosomes.（4marks）

（e）Suggesthowinducedmutationsinmancouldbeguardedagainst.（2marks）

HKALE1993BiologyPaperII

1.（a）Distinguishbetween

（i）codonandanticodon

（ii）continuousanddiscontinuousvariation（4marks）

（b）Theoccurrenceofcolourblindnessandhaemophiliainafamilyisshownbythepedigreebelow.ThegenesforthetwotraitsarefoundontheXchromosome

（i）Deducethedominanceorrecessivenessofthegenewhichleadsto

（1）colourblindness.

（2）haemophilia.

Explainyouranswer.

（Note:

GeneticdiagrarnswillNOTbeaccepted.）（6marks）

（ii）UseappropriatesymbolstorepresentthegenotypesofindividualsA,B,C,DandE.Defineallthesymbolsusedinyouranswer.（7rnarks）

（iii）IfindividualFmarriesanormalman,whatistheprobabilitythathersonmightbeahaemophiliac?

Withtheaidofageneticdiagram,explainyouranswer.（3marks）

HKALE1994BiologyPaperI

13.ResponsetoherbicidetreatmentisaninheritabletraitincertainplantspeciesApurelineplantspecies"

Topas"

（T）issensitivetoherbicide.AftermutationwasinducedinT,twohomozygousmutantlines（AandB）wereproducedwithdifferentresponsestoherbicidetreatment.

ThefollowingtableshowsthephenotypesofT,A,BandtheirF1plants:

Phenotypes

Sensitive

[S]

Lowtolerance

[LT]

Moderatetolerance[MT]

High

tolerance[HT]

T

ˊ

－

A

B

F1（A×

T）

F2（B×

Key:

ˊexpressionofphenotype

－noexpressionofphenotype

（a）Deducethegeneticbasisofinheritanceoftheherbicideresponseswithrespecttotheconceptofdominance.UsethistoexplaintheresponsesoftheF1,plantstotheherbicide.（6marks）

（b）MutantAandmutantBwerecrossedtoobtainF1,plants.TheseF1,plantswereselfedtoproduceF2plantsandtheirphenotypesareshowninthefollowingtable:

PhenotypesofF2（A×

B）

Numberofplants

9

18

27

90

（i）WhatistheF2（A×

B）phenotypicratio?

Basedonthisratio,determinethenumberofgenesinvolvedintheinheritanceoftheherbicideresponsetrait.

（ii）Usingappropriatesymbols,statethegenotypesof"

mutantAandmutantB.

（6marks）

（c）Basedontheinformationyouhavesofar,statethegenotypesfortheF1,plantsofthefollowingcrosses:

（i）mutantAand"

（ii）mutantBand"

（2marks）

（d）Suggestamethodforinducingmutation.（1mark）

（Total:

15marks）

HKALE1995BiologyPaperI

11.Ahorticulturistcollectedawildplantwithgiantflowersandlonginternodes.Hecrosseditwithahomozygouscultivar（acultivatedvarietyofthesamespecies）whichhadsmallflowersandshortinternodes.IntheF1progenyofthiscross,twophenotypicclasseswereobtained.Theywereplantswithgiantflowersandlonginternodesandplantswithsmallflowersandlonginternodes.Thephenotypicratiowas1:

1.

（a）Statetherecessivenessordominanceofthecharacters:

giantflowers,shortinternodes.（2marks）

（b）Ifthegenesfor"

flowersize"

and"

internodelength"

werelinked,wouldthesameF1phenotypicratio（1:

1）asmentionedabovebeobtained?

Explainyouranswerwiththehelpofageneticdiagram.（4marks）

（c）Giantflowersappealtoconsumers.Shortinternodesenablethepackingofmoreplantswithinacontainerfortransport.Therefore,bothpropertiescanincreasetheprofitfromthesaleofsuchplants.

（i）Giventhatthegenescontrollingthetwocharactersarenotlinked,

（1）statethepossiblegenotype（s）oftheplantswiththedesirablepropertiesmentionedabove,（1mark）

（2）designabreedingprogrammetoobtainaplantwithgiantflowersandshortinternodesbyselectingparentalplantsfromamongstthecultivarandthetwoclassesofF1plants.Explainthegeneticbasisofyourprogramme.

（Donotincludegeneticdiagramsinyouranswer.）

Note:

Thisplantspeciescanundergobothselfandcrosspollination.（4marks）

（ii）Whatpracticalstepswouldyoutaketoensurethetypeofpollinationinthecrosssuggestedinyourprogrammein（i）

（2）?

（iii）Bothvegetativepropagulesandseedscanbeproducedfromaplantwithgiantflowersandshortinternodes.Whichoftheseproductswouldyouselltoguaranteethatthesedesirablepropertieswillappearinthenextgeneration?

Explainyourchoice.（1marks）

（Total:

HKALE1997BiologyPaperII

3.（a）Whataretheprocessesthatgenerategeneticvariationsinfloweringplants?

Explainthemechanismsinvolved.（6marks）

（b）Adiploidplantbearsadominantmutationinonealleleofagenewhichcontrolssepalform.Thismutationhastheeffectofchangingscale-likesepalstopetal-likesepals.

（i）Astheflowerswithpetal-likesepalshaveabetterappealtocustomers.aplantbreederkeptthismutantplantinagreenhouseallowingittoself-fertilizeforseveralgenerations.Duringthisperiod.theplantbreedermadefrequentvisitstothegreenhouseandremovedanyplantbearingflowerbudswithscale-likesepals.DeduceandexplainthegenotypesoftheremainingplantsintheF1andF2populationsandtheirrelativeproportions.Whatwillbethelongtermeffectofthisbreedingpractice?

（7marks）

（ii）Theoriginalmutantplantwascrossedwithanotherplantwhichproducedflowerswithredpetalsandscale-likesepals.AlltheF1plantsshowedredpetals.Yetonlyhalfofthemproducedpetal-likesepals.WhentheseF1plantswereintercrossed,theF2progenyshowedapetalcolourratioof3:

1（threered-petal-bearingplantstoonewhite-petal-bearingplants）.Withoutusinggeneticdiagrams.deduceandexplainthedominantpetalcolourandthegenotypesofthetwoparents.（7marks）

HKALE1998BiologyPaperIB2

12.Thenumberofdaystakenfortomatoplantstoyieldripenedfruitsfromthedayofplantingisahereditarycharacter.Fourvarietiesoftomatoplantswereplantedinthesamefieldinthesameseason.Thefourvarietiesplantedwerethetwopure-bredparentalvarieties,P1andP2,theirF1hybridsandF2offspring.Thenumberofdaystakentoyieldripenedfruitsfor100plantsofeachvarietywasrecordedinthefollowinghistograms:

13.

（a）Whatisthetermusedtodescribetherangeofphenotypesobserved?

Whattypeofinheritanceisresponsibleforthis?

（b）Compareandcontrastthevariationsinthephenotypesof

（i）theF1hybridsandtheparents,P1andP2.Whatisthegeneticbasisforthedifference（s）?

（ii）theF1hybridsandF2offspring.Accountforyourobservations.（4marks）

（c）Toobtainvalidresultsinthisgeneticstudy,twofactorswerekeptundercontrolint