Transcript CHAPTER 18 CLASSIFICATION

CHAPTER 18
CLASSIFICATION
SECTION 1
FINDING ORDER IN DIVERSITY
KEY CONCEPT QUESTIONS:
 How are living things organized for
study?
 What is binomial nomenclature?
 What is Linnaeus’s system of
classification?
 How are living things organized for
study?
 To study the diversity of life,
biologists use a classification system
to name organisms and group them
in a logical manner
 TAXONOMY
 discipline of classifying organisms
and assigning each organism a
universally accepted name
Classification
 System to organize all living creatures
plants
 animals
 microbes
 etc.

 Why do you classify anything?
 to be certain everyone is talking about
the same thing
 Using common names can be
confusing
 In the United Kingdom, the word
buzzard refers to a hawk, whereas in
many parts of the United States,
buzzard refers to a vulture.
 Woodchuck and ground hog are the
same animal
Why not use common names?
 Misleading
starfish
 dragonfly
Confusing
 blue jay, blue coat,
corn thief
 dog, perro, chien


I swim,
but I’m still
a bird!
Why not use common names?
 But they all
have only
one scientific
name!
Pyrrhosoma nymphula
Cyanocitta cristata
Pisaster ochraceus
 A more universal way of scientifically
classifying came about
 BINOMIAL NOMENCLATURE
 classification system in which each
species is assigned a two-part
scientific name
Carolus Linnaeus
 The Linnean system
proposed in 1700s
 each species has a
2 part name
 genus
 species

Homo sapiens
Latin binomial
 2 part scientific name
Genus — larger group to which organism
belongs
 always capitalized
 species — specific name for that organism
 always lowercase
 example: Linnaeus named humans Homo
sapiens
 means “wise man”
— perhaps in a show of hope & optimism


The grizzly bear is called Ursus
arctos.
 The first part of the scientific
name—in this case, Ursus—is the
genus to which the organism
belongs
 The second part of a scientific
name—in this case, arctos—is
unique to each species within the
genus (this is usually a Latin name)
 GENUS
a group of closely related species
 Linnaeus’s System of Classification
 TAXON
 a group or level of organization;
aka: taxonomic category

Genus groupings
 Classify organisms into broader
groups
 Species that are closely related are
grouped into the same genus
 Leopard
Panthera pardus
 African lion
Panthera leo
 Tiger
Panthera tigris
Classification
 Kingdom
 Phylum
 Class
 Order
 Family
 Genus
 species
Orders & families
KEY CONCEPT QUESTIONS:
 How are living things organized for
study?
 Taxonomic categories
 What is binomial nomenclature?
 2-part universal naming system
 What is Linnaeus’s system of
classification?
 each species has a 2 part name
 genus
 species
SECTION 2
MODERN EVOLUTIONARY
CLASSIFICATION
KEY CONCEPT QUESTIONS:
 How are evolutionary relationships
important in classification?
 How can DNA and RNA help
scientists determine evolutionary
relationships?
 Darwin's ideas about descent with
modification have given rise to the
study of PHYLOGENY, or evolutionary
relationships among organisms.
 evolutionary history of a species
 based on common ancestries
inferred from
 fossil record
 morphological & biochemical
resemblances
 molecular evidence
 With the help of newer technology
scientists have found more accurate ways
of classifying organisms
 Biologists now group organisms into
categories that represent lines of
evolutionary descent, not just physical
similarities.
 In other words, species placed within the
same genus should be more closely
related to one another than to species of
any other genus
 EVOLUTIONARY CLASSIFICATION
method of grouping organisms
together according to their
evolutionary history
 To refine the process of
evolutionary classification, many
biologists now prefer a method
called cladistic analysis

 Cladistic analysis identifies and
considers only those characteristics of
organisms that are evolutionary
innovations—new characteristics that
arise as lineages evolve over time.
Characteristics that appear in recent
parts of a lineage but not in its older
members are called DERIVED
CHARACTERS.
Illustrating phylogeny
 Cladograms
patterns of shared characteristics
 diagram that shows the evolutionary
relationships among a group of organisms

Classify organisms
according to the order
in time at which
branches arise along
a phylogenetic tree
How is a cladogram constructed?
 Procedure : pg. 453 in textbook
 Identify the organism in the table that is least

closely related to the others.
Use the information in the table to construct
a cladogram of these animals.
Analyze and Conclude:
 What trait separates the least closely
related organism from the other
animals?
 Lack of backbone
 List the animals in your cladogram in
order of distance from the least
closely related organism.
 Trout, lizard, and human

Does your cladogram indicate that lizards and
humans share a more recent common ancestor than
either does with an earthworm? Explain.

Yes, lizards and humans shared an ancestor that
had legs and a backbone and that evolved after
the earthworm’s lineage branched off on another
evolutionary pathway
 Where would you insert a frog if you added it to the
cladogram? Explain your answer

A frog would occupy a branch between the trout
and the lizard, because it has the derived
characteristic of legs. Another derived
characteristic, such as dry skin, would then have
to be added for the lizard.
How are genes used to help scientists
classify organisms?
 The genes of many organisms show
important similarities at the molecular
level.
 The similarities can be used to help
determine classification
 Scientists compare the DNA of different
organisms to establish similarities
between them and reconstruct possible
evolutionary relationships
Of Mice and Men…
 Evolving genomes

now that we can compare the entire genomes of
different organisms, we find…
 humans & mice have 99% of their genes in
common
 50% of human genes have a close match with
those of yeast!
 the simplest eukaryote
 The more similar the DNA sequences
of two species, the more recently
they shared a common ancestor, and
the more closely they are related in
evolutionary terms
 Comparisons of DNA can also be
used to mark the passage of
evolutionary time.
 A model known as a MOLECULAR CLOCK
uses DNA comparisons to estimate the length
of time that two species have been evolving
independently.
 To understand molecular clocks, think about
a pendulum clock. It marks time with a
periodically swinging pendulum.
 A molecular clock also relies on a repeating
process to mark time—mutation.
Molecular clocks
•Trace variations
in genomes to date
evolutionary
changes
•Rate of change is
calculated and
then extrapolate
back
HIV-1M samples were collected from
patients between early 1980s & late
1990s. The gene evolved at a relatively
constant rate. Concluded that HIV-1M
strain first infected humans in 1930s.
Simple mutations occur all the time,
causing slight changes in the structure of
DNA
 Some mutations have a major positive or
negative effect on an organism's
phenotype.
 These mutations are under powerful
pressure from natural selection.
 Other mutations have no effects on
phenotype. These neutral mutations
accumulate in the DNA of different species
at about the same rate.

A comparison of such DNA
sequences in two species can
reveal how dissimilar the genes
are.
 The degree of dissimilarity is, in
turn, an indication of how long ago
the two species shared a common
ancestor.

Evaluating molecular homologies
 Aligning DNA
sequences
 more bases
in common =
more closely
related
 analyzed by
software
Modern Systematics
 Shaking up some trees!
Crocodiles are
now thought to
be closer to
birds than other
reptiles
KEY CONCEPT QUESTIONS:
 How are evolutionary relationships important in
classification?
 evolutionary history of a species based on
common ancestries inferred from
 fossil record
 morphological & biochemical resemblances
 molecular evidence
 How can DNA and RNA help scientists determine
evolutionary relationships?
 The more similar the DNA sequences of two
species, the more recently they shared a
common ancestor, and the more closely they are
related in evolutionary terms
SECTION 3
KINGDOMS AND DOMAINS
KEY CONCEPT QUESTIONS:
 What are the six kingdoms of life as
they are now identified?
 What is the three-domain system of
classification?
 Since Linnaeus’s time kingdom
classification has changed.
 he had two kingdoms – plantae
and animalia
 now there are six
 eubacteria, archaebacteria,
protista, fungi, plantae, and
animalia
 There is also a level higher than kingdom called

Domains
The three domains are:
 Bacteria
 kingdom Eubacteria
 Archaea
 kingdom Archaebacteria
 Eukarya
 Kingdom protists, fungi, plants, and
animals.
Universal Tree of Life
 3 Domains
Bacteria
 Eukarya
 Archaea

KEY CONCEPT QUESTIONS:
 What are the six kingdoms of life as
they are now identified?
 eubacteria, archaebacteria, protista,
fungi, plantae, and animalia
 What is the three-domain system of
classification?
 Bacteria
 Archea
 Eukarya