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Chapter12Introduc1ontoGene1cs

12-1TheworkofGregorMendel

•  GregorMendel•  AustrianMonk• Workedwithpeaplants

•  A.TrueBreedingPeaPlants– Self–pollinateandproducenewplantsgene1callyiden1caltothemselves

– Mendeldecidestocrosspollinatetheplants– Offspringarehybrids– Mendelstudiedtraits

•  1.seedshape•  2.seedcolor•  3.seedcoatcolor•  4.Podshape•  5.PodColor•  6.Flowerposi1on•  7.Plantheight

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GregorMendel’sPeas

Mendelknewthat

• themalepartofeachflowerproducespollen,(containingsperm).

• thefemalepartoftheflowerproduceseggcells.

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Copyright Pearson Prentice Hall

GregorMendel’sPeas

Thisprocessiscalledcross-pollina1on.

Mendelwasabletoproduceseedsthathadtwodifferentparents.

Copyright Pearson Prentice Hall

GenesandDominance

Mendel’s Seven F1 Crosses on Pea Plants Mendel’s F1 Crosses on Pea Plants

! 2Conclusions!  1.Traitsarepassedfromonegenera1ontothenextbygenes

•  Differentformsofgenesarecalledalleles

!  2.DominancePrinciple•  Someallelesaredominantandsomeallelesarerecessive

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•  B.Segrega1on– Parentplants=Pgenera1on

–  Crossfer1lizeparents,theoffspringarecalledF1genera1on– WhenF1plantsflower,2allelesaresegregatedsothateachgamete(pollenoregg)hasonecopyofthatgene.

– Tt"EggT" Pollent

SUMMARY

12-2ProbabilityandPunne]Squares

! Mendelfound:!  Hybridcrossedwithahybrid(Tt)createdabout¾talland¼short

! I.Gene1csandProbability" Thelikelihoodthatapar1culareventwilloccur" ThePrincipleofProbabilitycanbeusedtopredicttheoutcomeofgene1ccrosses

•  II.Punne]Squares– Canbeusedtopredictandcomparethegene1cvaria1onsthatwillresultfromacross

–  Homozygous:TTor]–  Heterozygous:Tt

–  Phenotype:physicalappearance(tall/short)–  Genotype:theactualgenes(Tt/TT/])

12.3ExploringMendelianGene1csI.Independentassortment

•  2factorcross•  Followingtwodifferentgenesastheypassfromonegenera1ontothenext.

•  A.Twofactorcross:F1– Purebreedingplantsfor2traits– seedshapeandseedcolor

•  RRYYXrryy•  B.Twofactorcross:F2

– Theprincipleofindependentassortmentstate»  Geneswithdifferenttraitscansegregateindependentlyduringtheforma1onofgametes

•  (Dihybridcross)

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•  II.SummaryofMendel’sPrinciples– 1.Characteris1csarepassedfromparentstooffspringbygenes

– 2.Someallelesaredominantandsomearerecessive

– 3.eachadulthas2copiesofagenethatseparatewhengametesareformed.

– 4.Allelesfordifferentgenesseparateindependentlyofeachother.

•  III.BeyondDominantandRecessive– A.IncompleteDominance

•  Onealleleisnotdominantovertheother,sowegetablendofthe2

•  4o’clockflowers•  RedxWhite"Pinkfowers

– B.Codominance– Bothallelescontributetophenotype– WhitefeatherschickenXBlackfeatherschicken"Speckledfeathers

– C.Mul1plealleles– Morethan2allelesforatrait

– D.Polygenictraits– Havingmanygenes

•  Morethanonegeneinvolvedinproducingthephenotype

•  Skincolor

Differentcombina1onsofallelesresultinthecolorsshownhere. KEY

C = full color; dominant to all other alleles cch = chinchilla; partial defect in pigmentation; dominant to ch and c alleles ch = Himalayan; color in certain parts of the body; dominant to c allele c = albino; no color; recessive to all other alleles

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ReviewofMitosis

•  Purpose–Celldivisiontoproducenewcellseverywhereinthebodyexceptforsexcells.

•  Endresult:2gene1callyiden1caldaughtercells

Prophase Nuclearenvelopebreaksdown,centriolesandspindlesappear,chromosomesbecomevisible.

Metaphase Chromosomeslineupinthemiddleofthecell

Anaphase Chromosomesareseparatedintochroma1dsandpulledtooppositeendsofthecell

Telophase Nuclearenvelopere-forms,centriolesandspindlesdisappear,andcytoplasmbeginspinchingin.

Cytokinesis Celldividesinto2gene1callyiden1caldaughtercells

4 Stages of Mitosis: PMAT

12.4Meiosis

•  I.ChromosomeNumber– Ex:fruitfly 8chromosomes

•  Homologouschromosomes»  4chromosomesfromDad»  4chromosomesfromMom

Diploidvs. Haploid

FullsetofchromosomesEx:humans46fruitfly8

HalfsetofchromosomesEx:human23fruitfly4

•  II.PhasesofMeiosis

ProphaseI Homologouschromosomespairupandformtetrads******CROSSINGOVEROCCURS**********

MetaphaseI Chromosomeslineupincenterofthecell

AnaphaseI

Chromosomesarepulledtooppositeendsofthecell

TelophaseI

Nuclearenvelopere-formsandcellsdivide.2newcells

ProphaseII

Nuclearenvelopebreaksdown,centriolesandspindleform

MetaphseII

Chromosomeslineupinthemiddle

AnaphaseII

Chromosomesarepulledapartintochroma1ds.Chroma1dsarepulledintooppositeendsofthecell.

TelophaseII Cellsdivideandproduce4gene1callydifferentcells

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•  III.GameteForma1on– *Meiosisproducesgametecells

– Males–4viablespermscells–  Females–1viableeggcellsand3polarbodies

•  Summary

LinkageandGeneMaps

•  I.GeneLinkage– Chromosomesassortindependently,notindividualgenes

•  II.GeneMaps– Therela1veloca1onofeachknowngeneonachromosome

•  1.Iftwogenesareclosetogether,therecombina1onfrequencybetweenthemshouldbelow.

•  2.Iftheyarefarapart,therecombina1onfrequencyshouldbehigh.

Page280Whichwillyouhavemoreof? Purpleeyesandspeckwings orBrowneyesandspeckwings

****Browneyesandspeckwings(closertogether)*****

Summary