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Chapter 20

Biology 1201A Chapter Notes - Chapter 20: Dont, Reptile, Monophyly

Course Code
BIOL 1201A
Jennifer Waugh

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phylogenetic trees a hypothesis of the evolutionary relationship among various taxa, including:
-common ancestry
-modern (extant) and extinct taxa
-sequence of events
-relative relatedness of taxa
20.4- Phylogeny
-show the evolutionary history of a group of organisms
Phylogenetic trees: formal hypotheses identifying relationships among groups of organisms
-Useful systematic characters must be genetically independent, reflecting different parts of
organisms’ genomes.
Homologous characters- similar in their evolutionary history but not necessarily their function.
They reflect underlying genetic similarities, and the comparison of homologous characters can
indicate common ancestry and genetic relatedness.
-These characters emerge from comparable embryonic structures and grow in similar ways
during development.
-Nodes represent common ancestors that underwent cladogenesis ( an evolutionary splitting
event where a parent species splits into two distinct species, forming a clade) and produced two
descendant clades.
Analogous Characters: in different animals that serve the same function. They are
homoplasious phenotypic similarities that evolved independently in different lineages. Are a
result of convergent evolution.
Mosaic evolution: refers to the reality that in all evolutionary lineages, some characters evolve
slowly, while others evolve rapidly. Every species displays a mixture of ancestral characters (old
forms of traits) and derived characters (new forms of traits).
Out group comparison: used to distinguish ancestral forms from derived characters involves
comparing the group under study with more distantly related species constituting a group not
otherwise included in the analysis.
Creating a phylogenetic tree:
- Collect taxa into increasingly
inclusive (i.e. nested – when
two groups belong to two bigger
monophyletic groups) groups
-Monophyletic groups include
all taxa that descend from a
common ancestor
-We want this
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