A phylogeny is the evolutionary history of a species or
group of species.
Example-legless lizards look like snakes yet they are more
closely related to legged lizards than they are to snakes.
The phylogeny of legless lizardsdemonstrates this.
Systematics is the process used to classify organisms and
establish evolutionary relationships.
Systematics uses DNA, biochemistry, fossils, embryology to
establish phylogenies. The classification of organisms is
based on evolutionary relationships. Organisms are given
two names-Based on Latin. The first is the genus name,
the second is the species name. Related species are
grouped together in the same genera, related genera are
grouped together in the same family and so on. There are
three Domains based on ribosomal sequencing- Eukarya,
Archae, and Bacteria
Classification-Linnaen Classification is based on a
hierarchy. Each species has two names, based on Latin.
The first is the genus classification and the second is the
species name. The first genus is capitalized and the
species is lower case. Both names are italicized. Similar
genera are in the same family. Similar families are in the same order. Similar orders are in the
same class. Similar orders are in the same phyla. Similar phyla are in the same Kingdom.
Kingdoms are placed in domains.
A taxon is a taxonmic unit at any of these levels. Higher units of taxons are usually defined by
morpho-logical differences rather than bio-chemical differences. Phylogenic tree- is a branching
diagram that represents
evolutionary history. Often it
mirrors hierarchal classification of
an organism. Node #2 represents
the most recent common ancestor
of the weasel and dog family,
whereas node # 1 represents the
most recent common ancestor of
the canine genus.
Phylogenetic trees cannot
1.Does not indicate absolute age
of a species. It only indicates the
most recent ancestor.
2.It does not assume that one
taxon on a phylogenetic tree
evolved from the taxon next to it
or on the same level.
Homology versus AnalogyHomologous structures are
structures that have a close
evolutionary ancestor. These
structures may or may not have the same function.
Analogous structures are structures that have the same function but do not have a close
evolutionary ancestor.
The wing of a bat and the wing of bird are both used for flying. They differ in that the wing of a
bird uses feathers versus the bat uses the membrane of skin stretched across bones. These are
analogous structures. The bones found in the wing of a bat are much more like the bones found
in the hand of a chimpanzee. These are homologous structures.
Analogous structures result from two different species in two different environments with similar
selection pressures. The two plants below are not closely related but are very similar due to
similar selection pressures.
Homologies can be extended to DNA sequences. The more closely related two species are, the
closely their DNA sequences will be alike.
Cladistics is a systematic approach in classifying organisms. Organisms are placed in groups
called clades which includes
common ancestor with a particular unique trait. This unique trait is passed on to all of its
descendents. Therefore a clade contains the ancestor and all of its descendents.
Clades, like taxonomic ranks are nested within larger clades. A clade is only considered a taxon
IF it contains an ancestral all of its descendents. Taxon 1 is considered to be a clade whereas
taxon 2 and taxon 3 are not considered to be clades.
Monophyletic relationship in grouping is a true clade whereas paraphyletic grouping (b) will leave
out one or more descendant groups in this case J. Polyphyletic grouping (c) has two or groups
without a common ancestor. B is the common ancestor but it is left out.
Cladistics is based on SHARED ANCESTRAL CHARACTERS and SHARED DERIVED
CHARACTERS. Ex-Mammals have backbones but that is not unique to mammals. All
vertebrates have backbones and therefore the backbone is a shared ancestral character that
originated in the ancestor of the taxon. Hair is shared by all mammals but not the ancestors of
mammals thus hair is considered to be a shared derived character that separates them from all
the other taxa.
Clades, like taxonomic ranks are
nested within larger clades. This
shows how a cladogram is reflective
of classification and it hierarchal
nature.
Example hair is considered to be a
shared derived characteristic of all
mammals but not turtles and
retractable claws is a shared derived
characteristic of members of the
family Felidae (cat family) but not
found in wolves, horses or turtles.
Below is a chart containing SHARED
DERIVED CHARACTERS for a
variety of vertebrates and a cladogram
based on the chart. Lancets are
considered to be an outgroup in that
they diverged from the group before vertebrates evolved and do not have a vertebral column.
Lancets are closely related to vertebrates but are not in the ingroup.
Of course you
need to look at
many characters
to determine what
is related to what.
In phenetics, you
do not need to
determine what is
an ancestral trait
and what is a
shared derived
trait. You only
care about who appears most similar to whom at one point in time. Cladistics is generally
considered to be more reliable for the determination of evolutionary relatedness.
The first classification system created by Linnaeus
considered only two kingdoms, Plant and Animals.
Prokaryotes were considered plants because of their
stiff cell wall, and fungi were considered plants
because the grew in the ground like plants. Later it
was recognized that prokaryotes, protists, and fungi
were so different from plants, that there should be
five kingdoms.
Monera-prokaryotes
Protista-single-celled eukaryotes
Plantae-multicellular, eukaryotes that are autotrophs
Fungi- multicellular, eukaryotes that are absorptive
heterotrophs.
Animalia- multicellular, eukaryotes that are ingestive
heterotrophs
One challenge has been
evidence that there are two
distinct lineages of prokaryotes.
It is based on the sequencing
of the rRNA found in the small
subunit. One lineage of
prokaryotes is more closely
related to eukaryotes than it is
to the other lineage of
prokaryotes. Most taxonomists
now recognize the domain as
the largest taxon. The three
taxa at the domain level are the
Bacteria, Archae, and Eukarya.
Within those domains are super
groups. The kingdoms are
found within the super groups.
Of the five kingdoms only three
have survived-Animalia, Plantae, and Fungi. The Monerean and Protista kingdoms are no longer
recognized.