12-1 the work of gregor mendel chapter 12 introduc1on to ... bio chp 12.pdf · 12-1 the work of...
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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
Copyright Pearson Prentice Hall
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