Mendelian GeneticsI:MonohybridCrosses
Todaysissues:
I. Darwinsdilemma
II. Mendelssolution
III. Analyzingdihybrid crosses
II.Mendelssolution
Mendelwastryingtounderstandthebasicpatternsofinheritance
Two contrasting hypotheses:Twocontrastinghypotheses:
1.
2.
A.Gardenpeasasamodelorganismp g
1. Mendelstudied7characteristics,andcouldgrowindividualswith2
2 M ifi ll th 2 h t i t d i2.Morespecifically,the2phenotypesexistedinpure
B.Analyzingamonohybridcross(tallvdwarfgrowthhabit)
Mendelsprotocol:1 Cross pureline parentals to yield1.Crosspurelineparentals toyield
2.AllowF1stoselffertilize,toproduce
Mendelsresults:1 Phenotypes of F s:1.PhenotypesofF1s:
2.PhenotypesofF2s:yp 2
Mendel claimed that blending inheritance is not correct WhichMendelclaimedthatblendinginheritanceisnotcorrect.Whichobservation(s)supportsthisconclusion?
Mendelcouldclaimthatinheritanceofacquiredcharactersisnotcorrect Which observation(s) supports this conclusion?correct.Whichobservation(s)supportsthisconclusion?
Theothersixtraitsgavesimilarresults.Whywasthisimportant?
Reciprocalcrossesgavethesameresults.Whywasthisimportant?
C.MendelsModel:aseriesofpropositions/hypothesestoexplainhisresults.Whatevidencedidhehaveforthepclaimthat:
1 Inheritance is particulate1.Inheritanceisparticulate.
2.Eachindividualpeaplanthastwoallelesofeachgene
3.Individualscanbehomozygousorheterozygous
4.Someallelesaredominanttoothers;someallelesareirecessive.
NOTE:Dominanceandrecessiveness aredefinedONLYinftermsof
5.Duringgameteformationinaparent,pairsofallelessegregate(separate)andgointodifferentgametes(Eachgametecontainsonealleleofeachgene.)
Thisistheprincipleofsegregation.
Question: What are the gamete genotypes producedQuestion:Whatarethegametegenotypesproducedbyparentswiththefollowinggenotypes?PPPpXRXr A1A2 S+SPP Pp X X A1A2S S
6. Male and female gametes fuse to form a zygote6.Maleandfemalegametesfusetoformazygote
Eachoffspringhastwoalleles
Oneallelefromeachparent
D.DoesMendelsmodelwork?Interpretingthemonohybridcross
TT fatherxttmother
Wh t h h th F ff i lf f tili ?WhathappenswhentheF1 offspringselffertilize?Parentalgenotypes:Gamete genotypesGametegenotypes:F2 genotypes:
RatioofF2 genotypes:RatioofF2 phenotypes:
III.Analyzingtheinheritanceoftwotraits
Mendelsquestion:aretheallelesfordifferentgenestransmittedtogetherorindependently?
Theexperimentalcross:Purplefloweredtall(PPTT)xh fl f ( )whiteflowereddwarf(pptt)
Hypothesis 1: Alleles from different genes areHypothesis1:Allelesfromdifferentgenesaretransmittedtogether.
Predict the results of this cross, ASSUMING THAT ALLELES OF THEPredicttheresultsofthiscross,ASSUMINGTHATALLELESOFTHEDIFFERENTGENESSTAYTOGETHER.Parentalgenotypes:PPTTppttGGametegenotypes:F1 offspring:
GametesproducedbyF1 parents:F offspring from selfing:F2 offspring,fromselfing:
R ti f F h tRatioofF2 phenotypes:
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