CHAPTER1Mendel’sBreakthrough:Patterns,Particles,AndPrinciplesOfHeredity

Historypoints

1843,BruennCatholicmonastery

1847,priest

1851-1853,Uni.ofVienna

1863,completedhisexperiments

1865,analyzingandsummarizing

thedata

1866,“ExperimentsinPlantHybridization”

1900,rediscoveryofMendel’sLaw

GregorJohannMendel(1822-1884)

GregorJohannMendel(1822-1884),1866

“ExperimentsinPlantHybridization”Lawofdominance,segregationandindependentassortment

FrontpageofMendel’spapersuperimposedonaportraitofMendelGregorJohannMendel

1.Mendel’sStudyofHeredity

a.Mendel’sExperimentalOrganism,theGardenPeaGardenpea:

dicot,petal,pollen,self-fertilization,inbred,true-breedingVariety:

6-7feet-tall,greenseeds9-18inches-dwarf,yellowseeds(Trait)

Reason:

contrastingdifferenceskeepcarefulrecord

Mendel’sexperimentalorganism

TheGardenPeab.MonohybridCrosses:

ThePrinciplesofDominanceandSegregation

MonohybridCrossesConclusion:

genescomeinpairs

parentalstrains:2identicalcopiesofgenegametes:asinglecopyofagenezygote(F1):heterozygousSymbolicrepresentationThecrossbetweenYellowandgreenpeas

Thecrossbetweentallanddwarfpeas

SymbolicrepresentationSummarize:1.TheLawofDominance:

inaheterozygote,oneallelemayconcealthepresenceofanother.2.TheLawofSegregation:

Thetwoallelesforeachtraitseparate(segregate)duringgameteformation,

thenuniteatrandom,onefromeachparent,atfertilization.TheprincipleofIndependentAssortment

c.DihybridCrosses:F1F2PDihybridCrossesAcrossbetweenavarietyofpeaswithyellow,roundseedsandavarietywithgreen,wrinkledseedsSummarize:

3.TheLawofIndependentAssortment:

Duringgameteformation,differentpairsofallelessegregateindependentlyofeachother.1900:TheRediscoveryofMendel’sLaw(孟德爾)（科倫斯）（狄.弗里斯）（馮.切爾邁克）

AustriaGermanyHollandAustria

For34years,Mendelslawslaydormant-untested,unconfirmed,andunapplied.Thenin1900,16yearsafterMendel’sdeath.CarlCorrens,HugodeVries,andErichvonTschemarkindependentlyrediscoveredandacknowledgedhiswork.2.ApplicationsofMendel’sprinciples-

predicttheoutcomeofcrossesa.ThePunnettSquareMethodb.Theforked-linemethod

(1)

Theforked-linemethod(2)c.Theprobability

Multiplicationofprobability:

independentevent:e.g.roundandyellowseedsofgardenpeaAdditionofprobability:

mutuallyexclusiveeventoralternativeevents:e.g.greenoryellowseedsofgardenpeac.Theprobabilitymethod-ApplicationoftheprobabilitymethodtoanintercrossinvolvingonegeneApplicationoftheprobabilitymethod

AnintercrossinvolvingtwogenesAaBbxAaBbWhatfractionoftheprogenywillshowrecessivephenotypeforatleastonegene?aaB-A-bbaabb?

╳?+?╳?+?╳?=7/16Applicationoftheprobabilitymethod

AnintercrossinvolvingthreegenesAaBbCcDd╳AaBbCcDdWhatfractionoftheprogenywillbehomozygousforallfourrecessivealleles?(1/4)╳(1/4)╳(1/4)╳(1/4)=1/256Whatfractionoftheprogenywillbehomozygousforallfourgenes?(1/2)╳(1/2)╳(1/2)╳(1/2)=1/163.FormulatingandTesting

GeneticHypothesesSnapdragon

Hypotheses:Theflowercoloriscontrolledbyasinglegenewithtwoalleles,W(forred)andw(forwhite),andthatWwheterozygotesarepinkbecauseWisonlypartiallydominantoverw.PWW(red)×ww(white)↓F1Ww

(pink)intercrossed

↓F2WWWw

ww1:2:1

TheChi-SquareTest

Degreesoffreedom:3–1=2Thecriticalvalue=5.9910.776<5.991∴thehypothesesisnotrejected.X2testCalculationofx2valueToknowthedegreesoffreedomx2valuemustbecomparedtothecriticalvalueIfx2valueislessthanthecriticalvalue,thehypothesisisnotrejectedDistributionofax2statisticChi-Square5%CriticalValues4.MendelianPrinciplesinHumanGenetics

Pedigrees

MendelianSegregationinHumanfamilies-cysticfibrosise.g.1:BinomialProbabilitiesTwokindsofprogeny:PandQProbability:pq(q=1-p)ProbabilityofxinclassPandyinclassQ=[n