Biology 1001A Lecture Notes - Lecture 14: Ginkgo, Wrasse, Anisogamy

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BIO1001ALecture14WhySex?
Introduction
● Inmanyspeciestherearetwodistinctsexes:maleandfemale
● Otherspeciesreproduceasexuallyandareclonesofoneanother,onlyonegender
(female)
● Whiptaillizardsreproduceasexuallyinaprocessknownasparthenogenesis
○ Thelizardswillproducecloneoffspringgeneticallyidenticaltothemother
○ Theyneedtoengageinpseudocopulationtohavetheireggsdeveloped
● Asexualreproductionisrareamongvertebrates
○ Humansareobligatelysexualreproducers
Copulation?Reproduction?Recombination?Maleness/Femaleness?
● Alloftheabovetermsaresometimesthoughtofassynonymoustosex,butthey’renot
Sex,Recombination,GeneticDiversity
● Reproducingsexuallygeneratesnewcombinationsofalleles
○ AB,ab,Ab,aB
○ Wecangetnewcombinationsofallelesthroughmeiosisandfusionofgametes
● Offspringdistinctfromeitherparentand(usually)fromeachother
● Sexualreproductioncanbeasourceofgeneticdiversityinapopulation
● Whenreproducingasexually,alloffspringarecopiesofparents
● Sexualreproductionmakesoffspringgeneticallydistinctfromparentsandeachother
(Withtheexceptionofidenticaltwins,triplets,etc)
Canhavereproductionwithoutsex,canhave‘sex’withoutreproduction
● Ex.binaryfissioninsinglecelledbacterium
○ Norecombinationgoingon
○ Reproductionwithoutsex
● Ex.BacterialIndividualsaren’treproducing/producingdaughtercells,butexchange
geneticmaterialthroughconjugation
○ Pseudosexnewcombinationsofallelesbeingformed
Obligatelyasexual:
canonlyreproducebycloningthemselves
○ Ex.AmazonMollyfish
Obligatelysexual:
organismswithouttheoptionofcloningthemselves,canonly
reproducesexually
○ Ex.Humans
Facultativelysexualvs.asexual:
candoeithersexualorasexualreproduction
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○ Ex.Dependingontheconditions,plantsmayproduceoffshootsasexually,or
makeflowers/seedswithotherindividualssexually
● Alotofreproductionisasexual,andyoucanhaverecombinationintheabsenceof
reproduction
SexualReproductionmayinvolvedioecy(separatesexes)ormonoecy(hermaphrodites)
Dioecy:
Malefunctionandfemalefunctionarefoundindifferentindividuals
○ Everyindividualismaleorfemale,butnotboth
○ Sexesareseparate
○ Ex.humansandgingkotrees
● Hermaphrodites:
bothmaleandfemalefunctionisfoundinthesameindividual
Ex.Perfectrosesarehermaphroditeshavetheabilitytoproducebothovules
andpollen
Theplantasawholecanbebothsexesbutpartsoftheplantcanbemaleor
female
○ Simultaneoushermaphrodites:
producebothspermandeggsatthesametime
■ Ex.Rosesandseaslugs
Monoecycanbesequentialratherthansimultaneous
Sequentialhermaphrodite:
Anindividualisbornasonesexandchangesexwhenthey
reachathresholdbodysize
○ Certainfishhavenogeneticsexdeterminationbutchangesexwhentheyare
thelargestindividualintheirschool
● Clownfisharesequentialhermaphrodites:startofflifeasmale,butafterreachinga
thresholdbodysize,theyswitchsexandbeginmakingfemalegametes
SizeAdvantageModelofSexChange
● Balancingmaleandfemalefunction:when,andinwhatdirectionshouldanindividual
changesex?
○ Whenisitadvantageoustomakethatswitch?
● Relationshipbetweensizeandfitnessisdifferentformalesandfemales
○ Youwanttomaximizereproductivesuccessasamaleandfemale
● Protandry:
Startinglifeasmaleandconvertingtofemale(M→F)
○ Ex.Inclownfish,bothsexeshavebetterreproductivesuccesswithsize,but
clownfishfemaleshavemoretogainbybeingbigandmoretolosebybeing
small
● Protogyny:
Beginningasbeingfemale,andswitchingtomale(F→M)
○ Ex.Inbluestreakwrasse,abigmalehaspotentialtomatewithmanyfemales
anddefendagainstpredators
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