Biology 1001A Lecture Notes - Lecture 11: Dihybrid Cross, Endoplasmic Reticulum, Meiosis

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BIO1001ALecture11InheritanceinPopulations
Reviewoflastlecture
● AlternatealleleshavedifferentDNAsequence
○ Allele=changesinDNAsequences
● Mendelfiguredouthowtheseallelesareinherited
● Inheritanceinpunnettsquaresrelatestomeiosis
● Howallelesridethroughmeiosisonchromosomes/sexchromosomes
● Mendel’sdihybridcrossproducesthe9:3:3:1ratio:
○ 9:R_Y
○ 3:R_y_
○ 3:r_Y_
○ 1:rryy
● Genotypeswillalwaysbein9:3:3:1ratiobutphenotypesmayvary
● Phenotypesdeterminedbybiochemistryofhowgenetypesinteract(ex.Epistasis)
Whatisatruecharacteristicofdominantalleles?
● Whatdoesdominancereallymean?
Simutext:Mendelianpigs
● Brownpigswerebredwithbrownpigs,andblackpigswithblackpigs,toproduce
truebreedingbrownpigsandblackpigs(bothhomozygous)
○ SimilartohowMendelfertilizedpeasplantsuntiltheyaretruebreeding
○ Resultingpigsthatarenotpurebreedingareculled
● Thetruebreedingbrownpigsarecrossedwithtruebreedingblackpigs(Pgeneration)
● Sinceblackisthedominanttrait,alloffspringareblack(F
1
Generation)
● Alltheblackpigsoffspringarecrossedwitheachother(F
1
xF
1
)
● Resultingoffspringisfoundtobeina3black:1brownratio
Simutext:Biochemistrybehindpigcolour
● Skinandhairpigmentationresultsfrommelaninincellscalledmelanocytes
○ Melanocytesmakemelanin,packageitinmelanosomesandexporttheminto
nearbyskincells
● Forthisdemonstration,Therearetwodifferenttypesofmelanin:blackandred(no
brown)
○ Melanocytescanmakeonlyblackandredmelanin
○ Browncolourresultsfromtheproductionofblackand
redmelanin
● Howdocellsknowwhethertomakeblackorred?
● TheMC1Rgeneistranslatedintoamembranereceptor(aproteinthatsitsonthe
membrane)
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