BIS 2C Lecture Notes - Lecture 2: Chronogram, Monophyly, Polyphyly
27 Apr 2018
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Lect2 Tree…
Three Types of Phylogenetic Trees
Cladogram: Only relative branching order is shown and there isn't meaning to branch length
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Phylogram: branched length is proportional to amount of character change
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Chronogram: branch length is proportional to time
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Two Types of Tree Branching
Bifurcating trees: internal nodes give rise to two descendant branches
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Polytomies: internal nodes that give rise to multiple (3+) branches
Usually shows uncertainty in phylogenetic relationships
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Solving Problems with Polytomies
3 branched Polytomies
One organism may be more closely related to later species but not too different
from previous
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Two organisms are more similar to one another than other species
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8 way Polytomy
Requires investigation into over 100k possible trees (135,135 to be exact)
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Terms of Phylogenetic Groups
Monophyletic groups: also a clade; a group of organisms consisting of most recent common
ancestor (MRCA) and all its descendants
Number of clades or monophyletic groups = number of internal nodes
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Paraphyletic: include some but not all descendants of the MRCA
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Polyphyletic: excludes the MRCA altogether, random groups
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Terms of. Monophyletic Groups
Synapomorphies: Characteristics unique to a monophyletic group/clade
Due to common ancestry and ability to inherit traits from MRCA that are not shared
with other groups
Ex: mammals - 4 chambered hear, hair ,milk, mammary glands
Bird have same heart but got it by convergent evolutions
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Homology: traits inherited from common ancestor
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Distinction: 4 chambered hearts are homologous with mammals and birds separately
Hearts of mammals are not homologous with that of birds
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Phylogenetic Classification
Classification: naming taxa and placing in hierarchal system
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Biological classification
Species: binomial names with Genus and species names both italicized
Homo sapiens
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Groups of species (higher taxa): Linnaean classifying system gives uninominal
name/ranked hierarchy
Genus, family, order, class, phylum
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When classifying, must make sure it is by monophyletic groups b/c
More convenient if they can be identified by their common synapomorphies
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Non-monophyletic groups are historical artificial groups
Ex birds and reptiles
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Group Classification Terms
Sister groups: 2 clades/species that are closest related to one another, descend from single
node, originate as lineages at the same time
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Ingroups: taxa under study
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Outgroups: taxa that is very closely related by not understudy
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Ancestral Traits: traits that arise in common ancestor
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Derived Traits: traits that arise within in groups are derived traits
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*For a clade, the synapomorphies of the clade are ancestral characteristics within the clade*
Look at number 10 on the figure
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Phylogenetic Tree Concepts (2)
Wednesday, January 10, 2018
12:53 AM
Document Summary
Cladogram: only relative branching order is shown and there isn"t meaning to branch leng. Phylogram: branched length is proportional to amount of character change. Bifurcating trees: internal nodes give rise to two descendant branches. Polytomies: internal nodes that give rise to multiple (3+) branches. One organism may be more closely related to later species but not too different from previous. Two organisms are more similar to one another than other species. Requires investigation into over 100k possible trees (135,135 to be exact) Monophyletic groups: also a clade; a group of organisms consisting of most recent comm ancestor (mrca) and all its descendants. Number of clades or monophyletic groups = number of internal nodes. Paraphyletic: include some but not all descendants of the mrca. Due to common ancestry and ability to inherit traits from mrca that are not shared with other groups. Ex: mammals - 4 chambered hear, hair ,milk, mammary glands.
