Biology 1001A Lecture Notes - Lecture 13: Genetic Drift, Mutation, Gene Flow

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BIO1001ALecture13AgentsofEvolution
TermTest2
● Saturday,Nov.7,24pm
● RoomspostedonOWL
● Cumulative:testsoutcomesforCycles36,pluskeyoutcomesforCycles1&2
● Multiplechoicequestions;individualandcollaborativecomponents
● Q&AThursday,Nov5th,5:306:30,NS145.
Q:HowwillallelefrequencieschangeifW
RR
=W
SS
>W
RS
?
● Exampleofheterozygotedisadvantage
Ans:Whicheverallelehasahigherinitialfrequencywillcontinuetoincreasein
frequency;theotherallelewilldecreaseinfrequencyuntilitdisappearsfromthe
population
Q:HowwillallelefrequencieschangeifW
RR
=W
SS
<W
RS
?
● Exampleofheterozygoteadvantage
● Ans:BothRandSwillapproachanequilibriumfrequencyof0.5
● Maintainsgeneticvariationinthepopulation
Whyaretheeffectsofheterozygoteadvantagevs.disadvantagesodifferent?
● Inheterozygotedisadvantage,thelesscommonallelewilldecreaseinfrequency
● Howdoesthefrequencyofanalleleaffectthelikelihoodthatitwilloccurina
heterozygoteratherthanahomozygote?
○ Amorecommonalleleismorelikelytobefoundinitshomozygousform
■ i.e:Whenthefrequencyofanalleleishigh,itisfoundmostoftenin
homozygousgenotype
○ Rarerallelesarefoundmostofteninheterozygotes
■ Underconditionsofheterozygoteadvantage,rarerallelesincreasein
frequencyuntiltheyarenolongerrare
○ Commonallelesinheterozygoteadvantagedecreaseinfrequency
○ Inheterozygotedisadvantage,commonallelesincrease
● Fitnessofanallelecandependonitsrelativeabundance(frequency)
Fitnessofagenotype/phenotypemaydependonitsrelativeabundance
● Negativefrequencydependentselection
○ Many(visual)predatorsform‘searchimages’anddisproportionatelyeatthemost
commonpreytypes
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