the tree of life. why classify? we classify to make organisms easier to study. to study the...
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THE TREE OF LIFE
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WHY CLASSIFY?
• We classify to make organisms easier to study.
• To study the diversity of life, biologists use a classification system to name organisms and group them in a logical manner.• The field of taxonomy allows scientists
to classify organisms and assign each organism a universally accepted name in order to study the diversity of life.
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LINNAEUS’S SYSTEM OF CLASSIFICATION
• During the eighteenth century, Swedish botanist Carolus Linnaeus developed a two-word naming system called binomial nomenclature• Linnaeus often classified organisms based on similarities in structures and details of anatomy
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BINOMIAL NOMENCLATURE
• In binomial nomenclature, each species is assigned a 2-part Latin name• The name is always written in italics
with the 1st word is always capitilized• Example: Homo sapiens (humans)
• The 1st part of the name is the genus and the second part of the name is unique to each species within that genus
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LINNAEUS’S SYSTEM OF CLASSIFICATION
• Linnaeus’s system of classification uses 7 taxonomic categories (from largest to smallest):• Kingdom – largest & most inclusive• Phylum – includes many different organisms that
share important characteristics• Class – composed of similar orders• Order – composed of similar families• Family – genera that share many characteristics• Genus – a group of closely related species• Species – a group of individuals so similar that
they can breed and produce fit offspring
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HUMAN CLASSIFICATION
• Kingdom: Anamalia• Phylum: Chordata
• Subphylum: Vertebrata
• Class: Mammalia• Order: Primates• Family: Hominidae• Genus: Homo• Species: Homo sapiens
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KINGDOM Animalia
PHYLUM Chordata
CLASS Mammalia
ORDER Carnivora
FAMILY Ursidae
GENUS Ursus
SPECIES Ursus arctos
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PROBLEMS WITH TRADITIONAL CLASSIFICATION
• During Linnaeus’s time, scientists classified organisms based on their physical appearance…but today…we know that doesn’t always work.
• Ex: Dolphins Fish or Mammals?
• Remember Convergent Evolution sometimes organisms that are different from each other evolve similar body structures, due to the change in the environment.• This does not mean they need to be classified in the
same group…maybe they only evolved similar body structures!
• These situations make it very difficult for scientists to classify.
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EVOLUTIONARY CLASSIFICATION
• Biologists now group organisms into categories that represent lines of evolutionary descent, not just physical features• Evolutionary classification (phylogeny)
is the strategy of grouping organisms together based on their evolutionary history
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TRADITIONAL V/S EVOLUTIONARY CLASSIFICATION
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CLASSIFICATION USING CLADOGRAMS
• To refine evolutionary classification, biologists now prefer a method called cladistics• Cladistics considers only those characteristics that
are 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
• Characteristics that are shared by all members of a lineage are ancestral/primitive characters and should not be used when building cladograms.
• Cladogram – a diagram that shows the evolutionary relationships among a group of organisms; includes new characteristics that arise as lineages evolve.
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DERIVED CHARACTERISTICS
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ANATOMY OF THE CLADOGRAM
A B
C D E F G H
I
J
Paraphyletic group
Monophyletic group = clade
Synapomorphy (shared derived character)
Node (represents most recent common ancestor of two or more taxa)
Lineage (represents a sequence of ancestor-descendent populations)
Taxon
MONOPHYLETICGROUPS:
include ancestor & all descendents
PARAPHYLETIC GROUPS:
includes ancestor and some, but not all descendent
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MONOPHYLETIC CLADES
• A valid clade is monophyletic signifying that it consists of the ancestor species and all its descendants.
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OUTGROUPS
• Systematists use a method called outgroup comparison• To differentiate between shared derived and shared
primitive characteristics
• As a basis of comparison we need to designate an outgroup• which is a species or group of species that is closely
related to the ingroup, the various species we are studying
• Outgroup comparison• Is based on the assumption that homologies
present in both the outgroup and ingroup must be primitive characters that predate the divergence of both groups from a common ancestor
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PERFORMING OUTGROUP COMPARISON
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OUTGROUP COMPARISONS
• First, look at the animals we are studying and establish which characteristics that they share & which are unique to each individual species.
• Then use these derived characters to build your cladogram.
CELLS BACKBONE LEGS HAIR OPPOSABLE THUMB
Slug
Catfish
Frog
Tiger
Human
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Cells
Backbone
Legs
Hair
Opposable Thumbs
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THE THREE-DOMAIN SYSTEM
• Molecular analyses have given rise to the most current classification system – the Three Domain System• The 3 Domain System is the most recent classification
system and includes: • Bacteria• Archaea• Eukarya
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DOMAINS ARE BIGGER/MORE INCLUSIVE THAN KINGDOMS
Domains Kingdoms
Bacteria Eubacteria
Archaea Archaebacteria
Eukarya
Protista
Fungi
Plantae
Animalia
These 2 kingdoms used to be combined into one called “Monera”
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REMEMBER - THERE ARE 3 METHODS OF CLASSIFYING
ORGANISMS
• The 3 Domain System (most current)• Bacteria, Archae, & Eukarya
• The 5 Kingdom System (Whittaker)• Monera, Protista, Fungi, Plantae, Animalia
• The 6 Kingdom System – still used in conjunction with the 3 domain system
• Archaebacteria, Eubacteria, Protista, Fungi, Plantae, Animalia
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Classification of Living Things
Section 18-3
Go to Section:
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DOMAIN BACTERIA
• Kingdom: Eubacteria• Unicellular• Prokaryotic• Cell wall of peptidoglycan• Autotrophic or heterotrophic• Examples: Streptococcus, E. Coli
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DOMAIN ARCHAEA
• Kingdom: Archaebacteria• Unicellular• Prokaryotic• Cell walls w/out peptidoglycan• Autotrophic or heterotrophic• Methanogens & halophiles
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DOMAIN EUKARYA
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WHITTAKER’S FIVE-KINGDOM SYSTEM
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OUR CHANGING VIEW OF BIOLOGICAL DIVERSITY
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THE THREE DOMAIN SYSTEM
• Describes classification as:• Not all prokaryotes are closely related (not
monophyletic)• Prokaryotes split early in the history of living
things (not all in one lineage)• Archaea are more closely related to Eukarya
than to Bacteria• Eukarya are not directly related to Eubacteria• There was a common ancestor for all extant
organisms (monophyletic)• Eukaryotes are more closely related to each
other (than prokaryotes are to each other)