1. Animal Life Cycles 2. Structure of DNA in Eukaryotes and ......2. Structure of DNA in Eukaryotes...

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

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?

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

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:


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:


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:


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!

1. Animal Life Cycles 2. Structure of DNA in Eukaryotes and ......2. Structure of DNA in Eukaryotes...

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