Transcript Trees and Keys - University of Miami


A branching tree has often been used as a
metaphor for descent from a common ancestor.
Each branch point (node) represents
a common ancestor of everyone
above that node on the tree.
The end of every branch represents
The “final product” of that descent
From a common ancestor.
Aristotle believed that life
was organized in a
hierarchy
 But remember: Evolution
is NOT like a ladder
 There is no “pinnacle” of
evolution.
 Instead, evolution is more
like a branching tree.

A species’
phylogeny is its
evolutionary history.
 The base of the tree
is the common
ancestor
 The nodes are also
common ancestors
 A phylogeny is a
hypothesis.

The study of the
evolutionary
relationships among
organisms
 The goal: classify on
the basis of recency
of common descent
 i.e., who shared the
most recent
common ancestor?

The science of
naming and
classifying organisms
 The Father of
Modern Taxonomy:
Carl Linne
 (a.k.a. Carollus
Linnaeus)


Full title:
› Systema Naturae: Creationis telluris est gloria
Dei ex opere Naturae per Hominem solum.

This last part translates as
› "The Earth's creation is the glory of God, as
seen from the works of Nature by Man
alone.”
related species are grouped in the same genus
(plural, genera)
 related genera are grouped in the same family
 related families are grouped in the same order
 related orders are grouped in the same class
 related classes are grouped in the same phylum
(plural, phyla)
 related phyla are grouped in the same kingdom
 related kingdoms are grouped in the same domain


Carl Woese used ribosomal RNA to
determine that there were three major
groups of organisms that were EACH
descended from a common ancestor.
All the other
groups in the
hierarchy are
nested within
one of the three
DOMAINS.
A taxon (plural = taxa) is a group of
organisms related by evolutionary
descent from a common ancestor.
 The more closely related two species
are, the more similar characteristics they
will share.
 Species descended from a common
ancestor have shared, derived
characteristics (a.k.a. characters)

Every species has its own unique
scientific name
 It consists of its genus (capitalized)
 And species (lower case)
 The name is italicized.
 Homo sapiens


HOMOLOGOUS characters are shared
between species because they were
inherited from a common ancestor.

ANALOGOUS characters have a similar
function in two species, but were not
inherited from a common ancestor.

PRIMITIVE characters have been
inherited from a common ancestor, but
are not very changed from the ancestral
form.

Example: All vertebrates have a bony
tail posterior to the anus.
PRIMITIVE characters are also called
PLESIOMORPHIES.
 plesio means “near” in Greek


morph means “form” or “shape”

A symplesiomorphy is a primitive
character shared by two or more taxa.

Like the post-anal tail shared here.

DERIVED characters have been inherited
from a common ancestor, but have
diverged in form among species

Example: Great apes have reduced
tails, compared to other vertebrates.
DERIVED characters are also called
APOMORPHIES.
 apo means “away” in Greek.


morph means “shape” or “form”

A synapomorphy is a shared, derived
character.

Like the reduced tail shared only by
apes, not other primates.
1a – made of metal……………….go to 2
 1b – made of paper………………..go to 5
 2a – brown (copper)………………penny
 2b – silver……………………………go to 3
 3a – smooth edge…………………nickel
 3b – ridged edge………………….go to 4
 4a – torch on back………………..dime
 4b – eagle on back……………….quarter


Notice that they share some traits, but
some share more traits than others.

Your job: use the provided taxonomic
key to identify your pasta samples to the
correct “species”.

A good taxonomic key can reflect evolutionary
relationships by using shared, derived characters.

With various “species” of hardware.
Each team will create a phylogenetic tree
Each team will create a taxonomic key

MAY THE BEST TEAM WIN!

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