10-24 lecture notes

8
Inferring Ph logenetic Trees Inferring Phylogenetic Trees Td ti T oday s questions: I B ildi il I. Building trees tutorial II. The problem of homoplasy

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Page 1: 10-24 Lecture Notes

Inferring Ph logenetic TreesInferring Phylogenetic Trees

T d ’ tiToday’s questions:  

I B ildi i lI. Building trees tutorialII. The problem of homoplasy

Why do small populations become inbred?-Because eventually, all individuals become related.
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I. Reading treesHow does this differ from the Great Chain of Being? 

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I. Phylogenetic trees tutorial

Work in teams of 3. Middle person as the scribe (does the writing). As you work through the questions, bethe writing). As you work through the questions, be sure to explain your logic to each other. 

Please ask us for help, if you need it!

Traits that ancestors have are basal traits, groups are only basal if they are the ancestor themselves.
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MonotremesMarsupialsGolden mole, tenrecElephant shrewsElephant shrewsAardvarkElephantsHyraxes

Current

yDugong, manateesArmadillosAnteaterSlothsCurrent 

phylogeny of the mammals, 

SlothsFlying shrews, tree shrewsProsimiansMonkeys

estimated from DNA sequence data

ApesRabbitsRodentsMoles hedgehogsdata Moles, hedgehogsHyenas, weasels, wolvesSeals, sea lionsPangolinH hiHorses, rhinosCamels, pigs, cowsHippos, whales, dolphinsBats

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II. The problem of homoplasy (versus homology)

Examples of traits that are similar, but not because they were inherited from a common ancestor: 

• Body shape in dolphins and icthyosaurs• Flippers in penguins and sealsFlippers in penguins and seals• Eye position in crocodiles and hippos• Camera eye in octopus and vertebratesy p

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1. Is the fur of chimps and the hair of humans homologous?

2. Whales and dolphins have only traces of fur. Humans p yhave little hair. Are these trait losses homologous? 

3. What does the hypothesis of homoplasy predict about genetic and developmental similarity? 

Homologous because they have common ancestor. Mammal common ancestor has fur.Homoplasy because it's more likely that their common ancestor has fur, so they couldn't have loss it due to common ancestor. We just both have loss of hairs because both our environment selected for loss of fur/ hair. That they are only similar because the environment they live in are similar or very different but select for the same trait.
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What causes homoplasy?

I h l i l t it C t l ti d t• In morphological traits: Convergent evolution due to:

• Reversal (particularly(particularly important in DNADNA sequence data): 

Environments that make similar demands on species so they develop similar traits.