Pre-APBiology2017-2018

Unit7GeneticsReviewOutlineLT1-Icanexplaintherelationshipsamongalleles,genes,chromosomes,genotypes,andphenotypes.

Thistargetcoversapplicationofthevocabularywordsabove.Studyyourcompletedvocabularylistassignmentandrefertothediagramsbelow.

LT2-IcansummarizetheworkofGregorMendelandthegeneticprinciplesthatarosefromthatwork.• GregorMendelwasamonkthatstudiedpeaplantbreedinginthe1800’s

o Firstpersontohavecorrectideasaboutinheritanceo Experimentstookeightyears(1856-1863)andresultswerepublishedin1865.

• Usedpeaplantsashismodelorganismbecausetheygrewquicklyandwereeasytostudybecauseoftheirvarietyoftraits(roundvwrinkled,yellowvgreen,tallvshort)

o Hegrewover10,000peaplants,keepingtrackofprogenynumberandtype.o Mendelfiguredoutthatgenescomeinpairsandareinheritedasonefromeachparent.o Trackedthesegregationofparentalgenesandtheirappearanceintheoffspringasdominantor

recessivetraits.• Mendelconductedcrossesoftrue-breeding(homozygous)parentstoproduceaheterozygousF1generation,

whichwerethencrossedbacktothemselves(F1xF1)toproduceanF2generationthatshowedagenotypicrationof1:2:1.

• Mendel'sLawsofHeredity:

1)TheLawofSegregation:Eachtraitisinheritedbyagenepair.Parentalgenesarerandomlyseparatedsothatsexcellscontainonlyonegeneofthepair(meiosis).Offspringthereforeinheritonegeneticallelefromeachparentwhensexcellsfertilize.2)TheLawofIndependentAssortment:Genesfordifferenttraitsaresortedseparatelyfromoneanothersothattheinheritanceofonetraitisnotnecessarilydependentontheinheritanceofanother.3)TheLawofDominance:Anorganismwithalternateformsofagenewillexpresstheformthatisdominant.

LT3–IcancompleteMendeliangeneticsPunnettsquarequestions• MendelianPunnettSquaresfollowtheLawofDominance–onealleleisdominantandtheotherisrecessive.

Therecessivephenotypeisonlydisplayedbyanorganismwithahomozygousrecessivegenotype.o EXAMPLE:o DominantPhenotypecanbeAAorAaforgenotypeo RecessivePhenotypecanonlybeaa

• Monohybridcrossesshowthepossibleoffspringinacrossofonetrait.§ Genotypeprobabilitycanbe0outof4(0%),1outof4(25%),2outof4(50%),or4outof4

(100%)§ Phenotypeprobabilitycanalsobeanyoftheabove,orexpressedasaratio.

• Dihybridcrossesshowtheprobabilityofoffspringinacrossoftwotraits.§ Probabilityisnowoutofatotalof16.§ WATCHTHEAMOEBASISTERSVIDEOIFYOUSTILLARESTRUGGLETOSETUPTHESE

PROBLEMS!

LT4–IcancompleteNon-MendelianPunnettSquarequestions.

• Non-Mendelianinheritancereferstotraitsthatdonotfollowstandarddominant-recessivepatterns.Thisincludes:

o IncompleteDominance:Truebreedingphenotypesarehomozygous;heterozygousgenotypeproducesnewphenotypethatisanintermediate,ormixture,ofthetwo.Example:aredflowerisrepresentedbyRR,awhiteflowerisrepresentedbyWW,andtheheterozygousRWappearsaspink.

o Codominance:Someallelescanbeequallyexpressedwhenbothpresent,forexampleinhowtheAproteinandBproteinarecodominantinbloodtypesuchthataTypeABindividualexpressesbothproteins.Anotherexamplecouldbetheflowercolorscenario,whereredisRR,whiteisWW,andRWisred-and-whitesplotches.

o Epistatis:Theexpressionofsometraitsisdeterminedbygenesthatcan“turnon”and“turnoff”thephenotype,thisiscalledepistatis.Forexample,alpacascanbeblackortanintermsofwoolcolor,butthereisanothergenethatcontrolswhetherornotpigmentinthewoolappearsatall.

o Sex-Linked:SometraitsarelocatedontheXorYsex-chromosomesandthereforeareconsidered

sex-linked.Thegenderoftheindividualdetermineshowmanycopiesofthealleleanindividualinherits.RememberfemalesareXXandmalesareXY.

o Polygenic:Sometraits,suchaseyecolororheightinhumans,areinfluencedbymanygenesworkinginconjunction.Thisproducesawidearrayofpossiblephenotypes(i.e.therearemanydifferentshadesofbrowneyes).

LT5-Icansummarizehowgeneticabnormalitiescancausedisordersinanorganism,suchasnondisjunction.

• GeneticdisordersarecausedbymutationswithintheDNAsequences(substitutionorframeshiftmutations)orbyachromosomalabnormality(nondisjunction)

o Point/SubstitutionMutationExamples:Tay-SachsDisease,Hemophilia,Sickle-CellAnemiao ChromosomalAbnormalityExamples:DownSyndrome(Trisomy21),TurnerSyndrome(Monosomyx),

KlinefelterSyndrome(TrisomyXXY)• Nondisjunctionisthefailureofchromosomestoproperlyseparateduringgameteformationinmeiosis.This

resultsingameteswiththeimpropernumberofchromosomes(usuallyhavingoneextraoronemissing,n+1orn-1).

o ThiscanresultinTrisomy(3chromosomesinsteadof2ataspecificlocation)orMonosomy(1chromosomeinsteadof2ataspecificlocation).

o Itispossibletohavemorethan3chromosomesatalocation,butthisisuncommon.

• Chromsomalabnormalitiescanbeassessedusingakaryotype,whichisapictureofallchromosomesarrangedbylargesttosmallestandnumbered,withthesex-chromsomesappearinglast.Humanshave23pairs–1through22areautosomal(notsex-related)andthelastpairarethesexchromosomes(XXorXYinanormalindividual).

LT6–Icananalyzeapedigreecharttodeterminemodeofinheritanceforagiventrait.• Ahumanpedigreeshowsthepatternofinheritanceofatrait/geneacrossgenerations• Malesarerepresentedbysquaresandfemalesarerepresentedbycircles• Individualswiththetrait/genearecoloredinandthosethatdonothaveitareleftblank• Forrecessivetraits,known“carriers”wouldbehalfshaded• Genesarelocatedondifferentchromosomes:

o AutosomalInheritance:gene/traitisunrelatedtogender,NOTonasex-chromosome(effectsmalesandfemalesequally)

o Sex-LinkedInheritance:gene/traitisinheritedfromeithertheXortheYsexchromosome(effectseithermalesorfemalesmore)

• Manypatternsofinheritance,butforthisclassyoushouldknow:

Pa#ern 1: Autosomal Dominant • Onlyonecopyofadiseasealleleisnecessaryforanindividualtoexpressthephenotype.• Malesandfemalesaffectedequally.• Allaffectedindividualswillhaveatleastoneparentwhocarriesthediseaseallele.

Pa#ern 2: Autosomal Recessive •  Twocopiesofadiseasealleleisnecessaryforanindividualtoexpressthephenotype.• Malesandfemalesaffectedequally.•  Theparentsofanaffectedindividualmaynotaffectedbutaregenecarriers.

Pa#ern 3: X-Linked Dominant •  OnlyonecopyofadiseasealleleontheXchromosomeisnecessaryforanindividualtoexpressthephenotype.•  Malesandfemalesaffectedequally.• Whenafemaleisaffected,thereisa50%chancefortheoffspringtoinheritthediseaseallele.Whenamaleisaffected,allhisdaughterswillbeaffected,butnoneofhissonswillbeaffected.

Pa#ern 4: X-Linked Recessive •  TwocopiesofadiseasealleleontheXchromosomeisnecessaryforafemaletoexpressthephenotype,butonlyonecopyforamalesincethealternateYchromosomedoesnotinfluenceX-linkedtraits.

•  Malesaffectedmorefrequentlythanfemales.

•  Affectedmalestransmitthediseasealleletoalloftheirdaughters,whoarethencarriers,buttononeoftheirsons.

•  Womenareaffectedwhentheyhavetwocopiesofthediseaseallele.Alloftheirsonswillbeaffected,andalloftheirdaughterswillbeunaffectedcarriers.