Biology 1001A Lecture 10: Mendel

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BIO1001ALecture10Mendel
AlternatealleleshavedifferentDNAsequence
● Youinherited7580newmutationsfromparentsthattheydidn’teveninheritfromtheir
parents
● Whendothesedenovo
mutationshappensuchthattheyendupinyoubutnotin
parents?
● EventuallytrytobecomfortableusingbothIn/del
andallele
inthesamesentence
● Allelesaredifferentversionsofagene,andonewaytheymightbedifferentisSNP’s
Summaryofmainideasaroundgeneticvariation…
1. “Variation”meansdifferencesindoublestrandedDNAsequence
● Variation=doublestrandedchange
2. OriginisinherentinchemistryofDNA,enzymologyofreplication/repair/recombination/
cytoskeleton
● Anyofthesethingscanbehaveinanunusualwayandcreatevariation
3. Canbeinfluencedbyphysical,chemical,biologicalagents/conditions(ex.mobile
elements)
4. Originisundirected(withrespecttosurvivalvalue)
● Nomattertheoriginofvariation,itisnotdirectedintermsofwhatwillbegoodfor
thecell(cellsdonotknowwhatisgoodforthem)
5. Originisnotrandomlydistributedaroundgenome.
● Itisnotrandom,eachbaseisnotequallylikelytochange
6. Onlygermlinevariationisavailabletonaturalselection
Mendel:Thinklikeascientistinthe1850’s
● Mendelwasveryintelligent,andmadecrucialscientificdiscoveriesingeneticsdespite
hislackofunderstandingofmolecularbiology
● Hedidcontrolledexperiments,andusedquantitativeanalysis
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Peopleusedtobelievethatinheritancewasby“blending”
● Itwasassumedthatthechildrenofatallparentandashortparentwouldalways
produceachildofintermediateheight
● Otherexampleisskincolour
Polygenictraitsshowncontinuousvariationina
population
● Therearemultiplegenescontrollingatrait
(andformostgenesthatisthecase)
● Thereareseveralgenesinvolvedinthese
traitsthatappeartobeblendingbutitisactually
multiplegenes(Seefiguretotheright)
Carefulexperimentationwithcontrolled
crossesandquantitativeanalyses…
● ReferringtoMendel’sexperiments
● Usedtruebreedingplantsifdifferenttraitsandpreventedtheirselffertilizationto
beabletocrossthemwithoneanother(Seefiguretotheleft)
...ledtoanexplanatorymodel…
● Variationintraitsduetodifferentalleles
● Allelessegregaterandomlyintogametes
● Organismsinherittwoallelesforeachtrait
● Appearanceofheterozygotesdeterminedby
dominantalleles
Punnettsquaresinrelationtomeiosis
● Meiosismakingspores:Pp
genotypetoP
and
p
gametes
● DifferencebetweenbigP
andlittlep
isa
mutation/variationinDNAsequence
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