LG 4 Outline
Evolutionary Relationships and Classification
Goals of Systematics
Phylogenetic Trees –
Taxonomy –
The Linnaean System of Taxonomy
Binomial Nomenclature –
Taxonomic Hierarchy –
Traits Used in Classification
Morphological Characteristics –
Homologies –
Homoplasies (Analogies) –
Ancestral and Derived Characters –
Cladistics –
Molecular Phylogenetics –
AP Biology
Unit III
Evolution
Learning Goal 4
Describe how evolutionary
relationships are used to classify
organisms.
Goals of Systematics
• Reconstruct
phylogeny
(evolutionary history)
of a group of
organisms.
This history is
illustrated in
phylogenetic trees.
These identify likely
relationships among
species.
• Taxonomy, or the
identification and
naming of species is
the second goal.
Taxonomy also
places organisms into
a classification
scheme.
• Naming and
Classifying
Organisms
• Began with the
Swedish naturalist
Carolus Linnaeus in
the 1700’s.
The Linnaean System of Taxonomy
• He invented the system
of binomial
nomenclature. In this
system, each species is
assigned a two-part
Latinized name.
• The first part identifies a
group of species with
similar morphology,
called a genus.
• The second part is the
species (specific) name.
• Linnaeus also
developed a
taxonomic hierarchy
to arrange large
numbers of
organisms into more
inclusive groups.
• A family is a group of
genera (plural of genus)
that closely resemble one
another.
• Similar families are group
into orders.
• Similar orders are
grouped into classes.
• Similar classes are
grouped into phyla
(singular phylum).
• Each category of the
taxonomic hierarchy is
called a taxon.
• Similar phyla are
grouped into
kingdoms.
• All life on Earth is
classified into three
domains.
Traits Used In Classification
• Morphological
Characteristics
Visible, measurable
traits that distinguish
groups of organisms
from one another.
Reflect genetic
differences.
Are preserved in the
fossil record.
• Homologies
Similarities that result
from shared ancestry.
• Homoplasies
Phenotypic similarities
that evolved
independently in different
lineages.
Also know as analogies.
Systematists exclude
homoplasies from their
analyses.
• Ancestral and Derived
Characters
Ancestral characters are
old forms of traits.
Derived characters are
newer forms of traits.
All species exhibit a mix
of both types of
characters and they
provide information about
evolutionary
relationships.
Cladistics
• A more recent approach
to classification based
solely on evolutionary
relationships.
• Cladists group together
only species that share
derived characters.
• Phylogenetic trees
produced by cladists are
called cladograms.
Molecular Phylogenetics
• Mutations in some types
of DNA appear to arise at
a relatively constant rate.
Differences in the DNA
sequences of two species
can serve as a molecular
clock.
Large differences imply
divergence in the distant
past. Small differences
suggest a more recent
common ancestor.
• Since DNA provides a code for
the production of proteins,
these molecules can be
analyzed to determine possible
relationships between species.
• When two species exhibit
similar amino acid sequences
for the same protein,
systematists infer their genetic
similarity and evolutionary
relationship.
Maximum Likelihood Programs
• Statistical model that
constructs numerous
alternative phylogenetic
trees from molecular
data, and estimates how
likely it is that each tree
represents the true
evolutionary history.
• Sytematists then accept
the phylogenetic tree that
is most likely to be true
until more data are
available.
LG 4 Vocab
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
Systematics
Taxonomic Hierarchy
Homoplasies
Ancestral Characters
Derived Characters
Cladistics
Cladograms
Molecular Phylogenetics
Molecular Clocks
Analogous Structures