Transcript Chapter 18.2 Notes

CHAPTER 18.2
NOTES
Phylogenetics
■ Scientists who study systematics are interested in
phylogeny, or the ancestral relationships between species.
■ Grouping organisms by similarity is often assumed to
reflect phylogeny, but inferring phylogeny is complex in
practice.
■ Reconstructing a species’ phylogeny is like trying to draw a
huge family tree over millions of generations.
Phylogenetics, continued
■ Not all similar characteristics are inherited from a common
ancestor.
■ Consider the wings of an insect and the wings of a bird.
■ Both enable flight, but the structures of the two wings
differ.
■ Fossil evidence also shows that insects with wings existed
long before birds appeared.
Phylogenetics, continued
■ Through the process of convergent evolution, similarities
may evolve in groups that are not closely related.
■ Similar features may evolve because the groups have
adopted similar habitats or lifestyles.
■ Similarities that arise through convergent evolution are
called analogous characters.
Phylogenetics, continued
■ Grouping organisms by similarities is subjective.
■ Some scientists may think one character is important, while
another scientist does not.
■ For example, systematists historically placed birds in a
separate class from reptiles, giving importance to
characters like feathers.
Cladistics, continued
■ Cladistics is a method of analysis that infers phylogenies by
careful comparisons of shared characteristics.
■ Cladistics focuses on finding characters that are shared
between different groups because of shared ancestry.
■ A shared character is defined as ancestral if it is thought to
have evolved in a common ancestor of both groups.
■ A derived character is one that evolved in one group but not
the other.
Cladistics, continued
■ For example, the production of seeds is a character that is
present in all living conifers and flowering plants, and some
prehistoric plants.
■ Seed production is a shared ancestral character among
those groups.
■ The production of flowers is a derived character that is only
shared by flowering plants.
Cladistics, continued
■ A cladogram is a phylogenetic tree that is drawn in a
specific way.
■ Organisms are grouped together through identification of
their shared derived characters.
■ All groups that arise from one point on a cladogram belong
to a clade.
■ A clade is a set of groups that are related by descent from a
single ancestral lineage.
Cladistics, continued
■ Each clade is usually compared with an outgroup, or group
that lacks some of the shared characteristics.
■ The next slide shows a cladogram of different types of
plants.
■ Conifers and flowering plants form a clade.
■ Ferns form the outgroup.
Cladogram: Major Groups of
Plants
Inferring Evolutionary
Relatedness,
Morphological Evidence
■ Morphology refers to the physical structure or
anatomy of organisms.
Inferring Evolutionary
Relatedness, continued
■ An important part of morphology in multicellular species is
the pattern of development from embryo to adult.
■ Organisms that share ancestral genes often show
similarities during the process of development.
■ For example, the jaw of an adult develops from the same
part of an embryo in every vertebrate species.
Inferring Evolutionary
Relatedness, continued
Molecular Evidence
■ Scientists can now use genetic information to infer
phylogenies.
■ Recall that as genes are passed on from generation to
generation, mutations occur.
■ Some mutations may be passed on to all species that have
a common ancestor.
Inferring Evolutionary
Relatedness, continued
Evidence of Order and Time
■ Cladistics can determine only the relative order of
divergence, or branching, in a phylogenetic tree.
■ The fossil record can often be used to infer the actual time
when a group may have begun to “branch off.”
■ For example, using cladistics, scientists have identified
lancelets as the closest relative of vertebrates.
Inferring Evolutionary
Relatedness, continued
Inference Using Parsimony
■ Modern systematists use the principle of parsimony to
construct phylogenetic trees.
■ This principle holds that the simplest explanation for
something is the most reasonable, unless strong evidence
exists against that explanation.
■ Given two possible cladograms, the one that implies the
fewest character changes between points is preferred.
Scientific Naming of
Organisms
The first name is the organism’s genus.
The second name is the organism’s species.
The genus is always capitalized; the species
is always lowercase.
The entire name is either printed in italics or
underlined.
Scientific Naming of Organisms
Ex. What is the
scientific name of this
organism?
Its genus is Homo.
Its species is sapiens.
Its scientific name is
Homo sapiens.
Scientific Naming of Organisms
In longer names, the genus
name can be abbreviated
to a single capital letter.
For example, this organism
is known as Carcharadon
carcharias.
This can be shortened to C.
carcharias.
Scientific Naming of Organisms
So, what do you call this
organism?
Puma concolor!
Three Domains for all organisms
Bacteria
Eukarya
• common members = bacteria
• common members = eukaryotes
• contains Kingdoms: Eubacteria
• contains Kingdoms: Protista, Fungi,
Plantae, and Animalia
•
Archea
• common members = archea
• contains Kingdoms: Archaebacteria
Kingdoms are defined by the
following characteristics
 Cell type : prokaryotic or eukaryotic
 cell walls : have a cell wall or don’t have a
cell wall
 body type : unicellular or multicellular
 nutrition : autotrophic (makes their own
food) or heterotroph (gets
nutrition from other organisms)
Genetics : DNA, RNA, or proteins
SIX KINGDOMS
The Six Kingdoms
1. Eubacteria
Unicellular, prokaryotic
organisms.
They can be autotrophs or
hertertrophs.
Eubacteria have thick cell
walls.
Ex. Cyanobacteria,
E. coli
The Six Kingdoms
2. Archaebacteria
Unicellular, prokaryotic
organisms.
They can be autotrophs or
hertertrophs.
They live in very harsh,
extreme conditions, like
volcanoes or other places
without oxygen.
Ex. Methanogens,
thermophiles
The Six Kingdoms
3. Protista
Most are unicellular, eukaryotic
organisms.
Protists can be autotrophs or
hertertrophs.
Some plant-like; some animallike; some fungus-like
Live in moist environments
Ex. amoeba, algae,
paramecium
The Six Kingdoms
4. Fungi
Most are Multicellular, eukaryotic
organisms.
Fungi are heterotrophic
decomposers.
Absorbs nutrients obtained by
decomposing dead organisms
and wastes
Ex. mushrooms, mold, yeast,
penicillin
The Six Kingdoms
5. Plantae
Multicellular, eukaryotic organisms.
Plant cells have cell walls containing
cellulose.
Plants are autotrophic.
Photosynthesize.
Tissues organized into organs and organ
systems.
Instead of phyla, plants are classified into
divisions.
Ex. moss, ferns, trees, gymnosperms,
angiosperms
The Six Kingdoms
6.
Animalia
Multicellular, eukaryotic organisms.
Animal cells do not have cell walls.
Animals are heterotrophic.
Animalia is the largest of the six
kingdoms.
Tissues organized into organs and
complex organ systems.
Ex. insects, fish, YOU