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: