Biology 1001A Lecture Notes - Lecture 20: Phylogenetic Tree, Convergent Evolution, Body Plan

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BIO1001ALecture20Phylogeny(continued)
Outgroupcomparisonreliesonparsimony:simplestexplanationisbest
● Whichevertreerequiresthefewestevolutionarychanges(gainsorlossesofatrait),is
probablycorrect
○ Example:(Seefiguretotheright)
○ Usingthesharkastheoutgroup,ifthetrait is
presentintheoutgroup,andsomeof
ingroupbutnotall,itismorelikelythatthe
traitisancestralratherthanderived
○ Otherwisethetraitwouldhavederived
independentlytwotimes
● Parsimony=Occam’sRazor
○ Theideathatifyouaretryingtochoosetwoexplanationsforapattern,gowith
thesimplestone
○ Whicheverexplanationminimizestheamountofevolutionarychangesthat
happenedisthesimplestandmostlikelyexplanationinphylogeny
○ Wedon’tknowforsure,butitislikelythatthetraitisancestralusingassumption
ofparsimony
Usingparsimonytoevaluatecandidatetrees
● Outgroup
○ Shark:Nomilk.Nofur.Nowings.Nobeak.
● Ingroup
○ Chicken:Nomilk.Nofur.Wings.Beak.
○ Bat:Milk.Fur.Wings.Nobeak.
○ Chipmunk:Milk.Fur.Nowings.Nobeak.
● Useoutgroupcomparisontoseeifatraitisancestralorderived
● Inphylogenyonlytheshared,derivedtraitsintheingroupmatter
Whichtreeismorelikelytobecorrect?
● Treesdifferintermsofwhetherthebatismorecloselyrelatedtothechipmunkorthe
chicken
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● Whichphylogenyismoreparsimonious(simple)?
● Incladisticanalysis,notalltraitsareequallyinformative
● Whichtraitsaresynapomorphies?
○ Seelistoftraitsabove
ClickerQuestion:
Q:Is“havingabeak”asynapomorphy?
● Outgroup
○ Shark:Nomilk.Nofur.Nowings.Nobeak.
● Ingroup
○ Chicken:Nomilk.Nofur.Wings.Beak.
○ Bat:Milk.Fur.Wings.Nobeak.
○ Chipmunk:Milk.Fur.Nowings.Nobeak.
A:No.
Whilehavingabeakisaderivedtrait
,itisalsonot
ashared,butauniquetrai
tto
chickens.Havingabeakisnotausefultraittobemapped.
Synapomorphiesaresharedandderived
● Outgroup
○ Shark:Nomilk.Nofur.Nowings.Nobeak.
● Ingroup
○ Chicken:Nomilk.Nofur.Wings.Beak.
○ Bat:Milk.Fur.Wings.Nobeak.
○ Chipmunk:Milk.Fur.Nowings.Nobeak.
● Wings,furandmilkaresynapomorphiesbecausetheyaresharedandderived(relatively
recentinevolutionaryorigin)
ClickerQuestion:
Q:Whichtreeismostparsimonious?
A:TreeA(ontheleft)
displayingthebatandchipmunkasbeingmorecloselyrelatedThisis
becauseittakeslessevolutionarystepstomakethetree.
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