Chapter5Topics1.AnimalLifeCycles2.StructureofDNAinEukaryotesandProkaryotes!3.ReplicationofDNA(copyingofDNA)4.Makingproteins!
• Transcription-goingfromDNAtomRNA• Translation-goingfrommRNAtoprotein
5.Generegulation!6.SizinguptheGenome7.Mutations8.MitosisvsMeiosis(sexualreproduction)9.MendelandPunnettSquares
Chapter5FinalTopicMendelandPunnetSquaresEveryonewasinterestedininheritanceduring2ndhalfof1800sMostlypeoplebelievedinblendinginheritance.
Whatisblendinginheritance??
Imagineballsareindividualsfilledwithpaintandyoumimicmatingbyrandomlypullingthemoutofabuckettwobytwo….
Fig.1.Differencebetweentheoutcomesfromblendingandfromparticulateinheritance.Inpost-Mendelianterms,weassumeasingledialleliclocus,andhencethreediploidgenotypes(AA,blue;Aa,green;aa,yellow).Underparticulateinheritance,thepopulation'svariabilityispreservedfromgenerationtogeneration.Incontrast,theconventionalwisdomofDarwin'sdaysawoffspringinheritablendofparents'characteristics,hererepresentedastheaverageofthetwoparentalshadings.Theresultisthatthevariabilitydiminishesinsuccessivegenerations(thevarianceishalvedeachgenerationifmatingisatrandom)SCIENCEMAGAZINEB.MAY
Fig.1.Differencebetweentheoutcomesfromblendingandfromparticulateinheritance.Inpost-Mendelianterms,weassumeasingledialleliclocus,andhencethreediploidgenotypes(AA,blue;Aa,green;aa,yellow).Underparticulateinheritance,thepopulation'svariabilityispreservedfromgenerationtogeneration.Incontrast,theconventionalwisdomofDarwin'sdaysawoffspringinheritablendofparents'characteristics,hererepresentedastheaverageofthetwoparentalshadings.Theresultisthatthevariabilitydiminishesinsuccessivegenerations(thevarianceishalvedeachgenerationifmatingisatrandom)SCIENCEMAGAZINEB.MAY
Fig.1.Differencebetweentheoutcomesfromblendingandfromparticulateinheritance.Inpost-Mendelianterms,weassumeasingledialleliclocus,andhencethreediploidgenotypes(AA,blue;Aa,green;aa,yellow).Underparticulateinheritance,thepopulation'svariabilityispreservedfromgenerationtogeneration.Incontrast,theconventionalwisdomofDarwin'sdaysawoffspringinheritablendofparents'characteristics,hererepresentedastheaverageofthetwoparentalshadings.Theresultisthatthevariabilitydiminishesinsuccessivegenerations(thevarianceishalvedeachgenerationifmatingisatrandom)SCIENCEMAGAZINEB.MAY
WhywasMendelabletodeducethe“particulatepattern”whileotherswerestruggling?Imagineyouareinterestedininheritance…….Whatmeasurementscouldyoumakeonthepeopleinthisclass?
WhywasMendelsuccessful?Hewassuccessfulbecausehechose….• flowercolorispurpleorwhite• flowerpositionisaxilorterminal• stemlengthislongorshort• seedshapeisroundorwrinkled• seedcolorisyelloworgreen• podcolorisyelloworgreen
Hedidnotchoosetraitslike• numberofseedsperpod• podlength• podwidth• seedsperplant• seedweight• plantheight
Toreview…Mendelchosetotrackonlycharactersthatvariedinan“either-or”ratherthanamoreorlessmanner.Hisplantshadeitherpurpleorwhiteflowers,therewasnothingintermediatebetweenthesetwovarieties.
HadMendelfocusedinsteadoncharactersthatvaryinacontinuumamongindividuals-seedweightforexample-hewouldnothavediscoveredtheparticulatenatureofinheritance!
ConsideringallthatcanoccurinthepathwayfromgenotypetophenotypeitisamazingthatMendelcouldsimplifythecomplexitiestorevealthefundamentalprinciplesgoverningtransmissionofindividualgenesfromparentstooffspring!
1865MendelpublisheshisPARTICULATEVIEWofInheritance…
Almostcompletelyignoredeventhoughitwouldhavemadenaturalselectionworktodriveevolution!
WasnotuntiltheModernSynthesisthatMendel’sideascametogetherwithmathematicalmodelsofnaturalselection.
Reviewofterms…Whatisalocus?Whatarealleles?Foradiploidorganism,howmanyalleleswilltherebeateachlocus?Homozygous?Heterozygous?Dominant?Recessive?
Reviewofterms…Whatisalocus?Whatarealleles?Foradiploidorganism,howmanyalleleswilltherebeateachlocus?Homozygous?Heterozygous?Dominant?Recessive?
IFtheblackgumballisDOMINANTtothewhitegumball,thisindividual’sphenotypewouldbe(whatcolorwouldthebeifthegumballlocusaffectedfurcolor)…..?
Imagebelowshows5pairsofhomologouschromosomesin5differentindividuals.
Whichotherindividualsareheterozygousinthispopulationatthegumballlocus?Howmanyallelesarethereinthispopulationof5individualsatthegumballlocus?
Foradiploidorganism,howmanyalleleswilltherebeateachlocus?
Letsfocusonasinglelocus(“gene”)onasinglechromosomeforplants!
Inplantsweuseupperandlowercaseletters(usually).
Fromyourtext!Whichisdominant?
I’lladdanotherexample-FlowercolorinMendel’speasInpeaplantsP(purpleflowers)isdominantto(p)whiteflowers…..SoifaplantisPPitwillbe..whatcolor?IfitisPpitwillbe...Ifitisppitwillbe…
Parental generation (P)
PP pp
Genotypesofalloffspring(F1)?
Phenotypesofalloffspring?
What gametes? What gametes?
AnorganizedwaytorespondtothisquestionofwhatarethegenotypesgoingtobeinthenextgenerationistouseaPunnettSquare..PPxppcross…
Whataregenotypesandphenotypesofoffspring?
p p
P
P
AnorganizedwaytorespondtothisquestionofwhatarethegenotypesgoingtobeinthenextgenerationistouseaPunnettSquare..PPxppcross…
Whataregenotypesandphenotypesofoffspring?DidIevenneeda2x2table??
Pp
Pp Pp
Pp zygotes
p p
P
P
SotheseareallPp…right?Nowletscrosstwoofthese!
PP pp
F1
P
P
p
p
Whatifyouinterbredtheoffspring(F1)togettheF2?PpxPpcross…
WhataregenotypesandphenotypesoftheseF2offspring?
PP
Pp
Pp
pp
P
P
p
p
WhatifyouinterbredtheoffspringorF1togettheF2?PpxPpcross…
WhataregenotypesandphenotypesoftheseF2offspring?
Phenotype
1
Genotype
Purple
Purple
Purple
White
Ratio 3:1
PP (homozygous)
Pp (heterozygous)
Pp (heterozygous)
pp (homozygous)
Ratio 1:2:1
2
3
1
1
P Generation (true-breeding
parents)
F1 Generation
F2 Generation
Purple flowers White flowers
All plants had purple flowers
Self- or cross-pollination
705 purple-flowered plants
224 white-flowered plants
Isthisobservationcompatiblewithblending????
Thisreappearanceofwhiteflowerswasconsideredamazing!!Whitedisappearedandthenreappeared!
WasprettyimpressivethatthroughtheseresultsMendelwasabletoinferwhatwasgoingon!Hefiguredoutthatthereweretrue“particles”thatretainedtheiridentity.Wasnotlikepaintblending!
Toreview…Mendelchosetotrackonlycharactersthatvariedinan“either-or”ratherthanamoreorlessmanner.Hisplantshadeitherpurpleorwhiteflowers,therewasnothingintermediatebetweenthesetwovarieties.
HadMendelfocusedinsteadoncharactersthatvaryinacontinuumamongindividuals-seedweightforexample-hewouldnothavediscoveredtheparticulatenatureofinheritance!
ConsideringallthatcanoccurinthepathwayfromgenotypetophenotypeitisamazingthatMendelcouldsimplifythecomplexitiestorevealthefundamentalprinciplesgoverningtransmissionofindividualgenesfromparentstooffspring!
Gettingmorereal…..1.Mostreallocihavemanyalleleswhenyoulookatapopulation!• Bloodgroups…IA, IB, and IO
• Majorhistocompatibilitycomplex(MHC)genesalsoknownasthehumanleukocyteantigen(HLA)mayhaveonehundreddifferentallelesatasinglelocus!!!
2.Mostgenesaffectmultipletraits-Pleiotropy!Ex.CysticfibrosiscausedbymutationsinCFTRgene(Over1900alleles!)affectslungs-getinfectionsbutalsoaffectspancreasanddigestivesystem.Ex.Fruitfliesvggeneaffectswingsandthepositionofbristlesonafly'sscutellum,anddecreasesthelengthofafly'slife.
Insomecases…twoallelesataparticularlocushaveunusualrelationships!Itmaynotbeasimpledominant-recessiverelationship.
½ ½
P Generation
F1 Generation
Gametes
Gametes
White CWCW
Pink CRCW
Red CRCR
CW CR
CW CR
3.Incompletedominance!Isthisblendinginheritance???
Thischickenisheterozygousatasinglelocus(BW),erminette.
Whatisgoingonhere?Bothallelesareexpressed!
4.Codominance
Plusmanygenesinteractwithoneanother….
¼
¼
¼
¼
¼ ¼ ¼ ¼
BE
be
BBEE
bbee
BbEE BbEe
bE
Be
BBEe
BbEE bbEE bbEe BbEe
BBEe BbEe Bbee BBee
BbEe bbEe Bbee
9 : 4 : 3
Eggs
Sperm
Bb Ee FYI..2locion2differentchromosomesWhatwouldbethepossiblegenotypesofthespermproducedbythismalelab?
¼
¼
¼
¼
¼ ¼ ¼ ¼ BE Be
BE
be
BBEE
bbee
BbEE BbEe
bE be
bE
Be
BBEe
BbEE bbEE bbEe BbEe
BBEe BbEe Bbee BBee
BbEe bbEe Bbee
9 : 4 : 3
Eggs
Sperm
BbEe BbEe FYI..2locion2differentchromosomes
¼
¼
¼
¼
¼ ¼ ¼ ¼ BE Be
BE
be
BBEE
bbee
BbEE BbEe
bE be
bE
Be
BBEe
BbEE bbEE bbEe BbEe
BBEe BbEe Bbee BBee
BbEe bbEe Bbee
9 : 4 : 3
Eggs
Sperm
BbEe BbEe
¼
¼
¼
¼
¼ ¼ ¼ ¼ BE Be
BE
be
BBEE
bbee
BbEE BbEe
bE be
bE
Be
BBEe
BbEE bbEE bbEe BbEe
BBEe BbEe Bbee BBee
BbEe bbEe Bbee
9 : 4 : 3
Eggs
Sperm
BbEe BbEe
¼
¼
¼
¼
¼ ¼ ¼ ¼ BE Be
BE
be
BBEE
bbee
BbEE BbEe
bE be
bE
Be
BBEe
BbEE bbEE bbEe BbEe
BBEe BbEe Bbee BBee
BbEe bbEe Bbee
9 : 4 : 3
Eggs
Sperm
BbEe BbEe
Figure11.12
¼
¼
¼
¼
¼ ¼ ¼ ¼ BE Be
BE
be
BBEE
bbee
BbEE BbEe
bE be
bE
Be
BBEe
BbEE bbEE bbEe BbEe
BBEe BbEe Bbee BBee
BbEe bbEe Bbee
9 : 4 : 3
Eggs
Sperm
BbEe BbEe
Whatisgoingon????Brownlabwhenhomozygousrecessive(bb)andeither(EE)or(Ee).
¼
¼
¼
¼
¼ ¼ ¼ ¼ BE Be
BE
be
BBEE
bbee
BbEE BbEe
bE be
bE
Be
BBEe
BbEE bbEE bbEe BbEe
BBEe BbEe Bbee BBee
BbEe bbEe Bbee
9 : 4 : 3
Eggs
Sperm
BbEe BbEe Getyellowlabwheneveree!(Itshutsdowncolorproducinggene.)Whatisthiscalled?5.Epistasis
6.Traitsareusuallydeterminedbymanymorethanoneoreventwoloci!With2lociwhatismaximumnumberofgeneticallydifferentgametesyoucouldhave?BbEe 4differentgametes….(BE,Be,bE,be)
Imagine3lociormore!
Howmanygeneticallydifferentgametesarepossiblewith3lociallonseparatechromosomes?AaBbCcABCAbcABcaBCabCAbCaBcabcWhatwillyourpunnetsquarelooklike!!
Eggs
Sperm
AaBbCc AaBbCc
Phenotypes:
0 Number of dark-skin alleles: 1 2 3 4 5 6
1 64 1 64 6 64 6 64 1 64 15 64 15 64 20 64
1 8
1 8
1 8
1 8
1 8
1 8
1 8
1 8
1 8 1 8 1 8 1 8 1 8 1 8 1 8 1 8
Ex.SkincolorisPolygenic(quantitativetraitormultilocustrait)
Eggs
Sperm
AaBbCc AaBbCc
Phenotypes:
0 Number of dark-skin alleles: 1 2 3 4 5 6
1 64 1 64 6 64 6 64 1 64 15 64 15 64 20 64
1 8
1 8
1 8
1 8
1 8
1 8
1 8
1 8
1 8 1 8 1 8 1 8 1 8 1 8 1 8 1 8
ABC abc
Eggs
Sperm
AaBbCc AaBbCc
Phenotypes:
0 Number of dark-skin alleles: 1 2 3 4 5 6
1 64 1 64 6 64 6 64 1 64 15 64 15 64 20 64
1 8
1 8
1 8
1 8
1 8
1 8
1 8
1 8
1 8 1 8 1 8 1 8 1 8 1 8 1 8 1 8
Eggs
Sperm
AaBbCc AaBbCc
Phenotypes:
0 Number of dark-skin alleles: 1 2 3 4 5 6
1 64 1 64 6 64 6 64 1 64 15 64 15 64 20 64
1 8
1 8
1 8
1 8
1 8
1 8
1 8
1 8
1 8 1 8 1 8 1 8 1 8 1 8 1 8 1 8
Doyouthinkhaving3lociisrealisticforskincolor?
“Humanskincolorisapolygenictrait,meaningmultiplegenelociareinvolvedinitsexpression.Atlastcount,theInternationalFederationofPigmentCellSocieties…hasdeterminedthatthereareatotalof378geneticlociinvolvedindeterminingskincolorinhumansandmice.”http://www.gbhealthwatch.com/Trait-Skin-Color.php
7.Twolociorgenes(andthusthetraitstheycodefor)maybelinkediftheyareclosetogetheronthesamechromosome!Ifyouinheritoneyouverylikelyinherittheother-recombinationwillnotbreakthemapartduringmeiosis.
https://commons.wikimedia.org/wiki/File:Figure_17_02_01.jpg
8.MultifactorialtraitsWhenadiseaseissaidtohaveamultifactorialbasis,itmeansthat…???• itiscausedbyagenewithalargenumberofalleles• itaffectsalargenumberofpeople• ithasmanydifferentsymptoms• bothgeneticandenvironmentalfactorscontributetothedisease
• ittendstoskipageneration
8.MultifactorialtraitsWhenadiseaseissaidtohaveamultifactorialbasis,itmeansthat…???• itiscausedbyagenewithalargenumberofalleles• itaffectsalargenumberofpeople• ithasmanydifferentsymptoms• bothgeneticandenvironmentalfactorscontributetothedisease
• ittendstoskipagenerationComeupwithanexampleofamultifactorialdisease!Thesearethenorm!