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Lecture 19

BIOL 1201 Lecture Notes - Lecture 19: Punnett Square, Dihybrid Cross, Sickle-Cell DiseasePremium


Department
Biological Sciences
Course Code
BIOL 1201
Professor
Moroney, James
Lecture
19

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BIOL1201Lecture19GeneticsContinued
Dihybridcross
● twocharacters
● Gametescontainanalleleforeachtrait
Carriers
Heterozygous
Carriesgenetictraitbutdoesn’thavethediseasethemselves
Theiroffspringmayormaynotinheritthediseasegene
● WhatisthechanceI’macarrier?Mybrotherhassicklecellandmyparentsarecarriers
(Heterozygous)
HH
Hh
Hh
hh
Lookatpunnetbelow.Sincebrotherhasitandheisfine,heisobviouslydoesn’t
havethegene.Thatmeans thereisa2/3chanceheisacarrier.
● 3recessivehumangametediseases:sicklecellanemia,cysticfibrosis,andTaysachs
● Dominanthumangamete:dwarfism,Huntington’s
Calculationsusingprobabilities
Punnettsquareisaccuratebuttedious,fortwoormoretraits
Multiplicationofprobabilitiesforeachtraitisfasterandeasier
PhenotypeExample:Howmanyyellowroundindividualswouldbeproducedfrom
parentsheterozygousforeachtrait(YyRrxYyRr)?
GenotypeExample:HowmanyYyRrindividualswouldbeproducedfromparents
heterozygousforeachtrait(YyRrxYyRr)?
Forthesedividethealleles:sobasicallydotwoPunnettsquares.Oneforcolor,
oneforshapeandthenmultiplythetwofractionsyouget
Dothesameprocedureforthetrihybrid
MendelReview
Traitsaregovernedbytwoalleles,onecompletelydominantovertheother
Allelessegregateingametes
Fortwoormoretraits,allelesassortindependentlyduringgameteformation
IncompleteDominance
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