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Classification

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Why Classify?

• To study the diversity of life, biologists use a classification system to name organisms and group them in a logical manner.

• In taxonomy, scientists classify organisms and assign each organism a universally accepted name.

• By using a scientific name, biologists can be certain that everyone is discussing the same organism.

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Aristotle 384 BC

• Classified organisms as either plants or animals

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Carolus Linnaeus 1707-1778

• Classification system• Based on physical

structure• Taxonomic groups of

related organisms• Binomial nomenclature

(two names ex.Homo sapiens)

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Binomial Nomenclature

•  Carolus Linnaeus• In binomial nomenclature, each species

is assigned a two-part scientific name. – The scientific name is always written in italics

or underlined. – The first word (the genus) is capitalized – The second word (the species) is lowercased.EX- Genus species or Genus speciesHumans- Homo sapien

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Linnaeus's System of Classification

• A group or level of organization is called a taxonomic category, or taxon

• Linnaeus had 7-

Kingdom “King

Phylum Phillip

Class Came

Order Over

Family For

Genus Great

Species Spaghetti”

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Taxonomic Groups

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Classification of Man

• Kingdom Animalia

• Phylum Chordata

• Class Mammalia

• Order Primates

• Family Hominidae

• Genus Homo

• Species Homo sapiens

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Species

• “Species are groups of actually or potentially interbreeding populations, which are reproductively isolated from other such groups.”

• Reproductively isolated group

Ernst Mayr

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Different Species

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Checkpoint Questions:

1.  How are living things organized for study?

2. Describe the system for naming species that Linnaeus developed.

3. What are the seven taxonomic categories of Linnaeus’s classification system?

4. Why do scientists avoid using common names when discussing organisms?

5.  What is significant about members of the same species?

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Modern Evolutionary Classification 

• Organisms are grouped into categories that represent lines of evolutionary descent, not just physical similarities

Modern classification systems are based upon biochemical and genetic evidence that indicates evolutionary relationships

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Classification Using Cladograms• Cladistic analysis identifies and considers only the

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.– Derived characters can be used to construct a cladogram,

a diagram that shows the evolutionary relationships among a group of organisms.

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Cladogram

• Evolutionary relationship of a group of organisms

• Each clad (group) share something in common

• Ancestral traits are the oldest

• Derived traits evolved later

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Cladogram for Transportation

• Wheels are the most ancestral

• Wings are the most derived

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Construct a Cladogram

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Gorilla

• Four limbs• Fur• Lost tail

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Tiger

• Four limbs• Fur• Tail

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Lizard

• Four limbs• Tail

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Fish

• Tail

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Chimpanzee

• Four limbs• Fur• Lost tail

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Clad With 4 Limbs

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Clad With Fur

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Clad With No Tail

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Characteristics for Constructing Cladogram

• Tail is the most ancestral

• Four limbs is the oldest derived trait

• Fur is a later derived trait

• Loss of tail is the most derived trait

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Gorilla Chimpanzee

Tiger

Lizard

Fish

Four Limbs

Fur

Tail Lost

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Gorilla Tail?

• How do we know the gorilla lost its tail?

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Gorilla’s Vestigial Tail

Gorilla Human

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TRADITIONAL CLASSIFICATION

CLADOGRAM

Appendages Conical Shells

Crab Barnacle Limpet Crab Barnacle Limpet

Crustaceans Gastropod

Molted exoskeleton

Segmentation

Tiny free-swimming larva

Section 18-2Traditional Classification Versus Cladogram

Go to Section:

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Modern Evolutionary Classification 

• Similarities in DNA and RNA

– The genes of many organisms show important similarities at the molecular level that can be used as criteria to help determine classification.

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Modern Evolutionary Classification

• Molecular Clocks

– A model known as a molecular clock uses DNA comparisons to estimate the length of time that two species have been evolving independently.

• Comparison reveals more DNA in common, the more recent the common ancestor

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Terminology

• Classification– Assigning organisms to

different catagories based on their relationship

• Taxonomy– The science of naming

organisms

• Systematics– Determining evolutionary

relationships of organisms

• Phylogeny– Evolutionary history

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Phylogenetic Tree

• Shows evolutionary relationships

• More historical than cladogram

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MyxozoaMyxozoaMyxozoaMyxozoa

ArthropodaArthropodaArthropodaArthropoda AnnelidaAnnelidaAnnelidaAnnelida

MolluscaMolluscaMolluscaMollusca

LophophoratesLophophoratesLophophoratesLophophorates

HemichordataHemichordataHemichordataHemichordata

ChordataChordataChordataChordata

Other Other pseudocoelomatespseudocoelomates

Other Other pseudocoelomatespseudocoelomates

NematodaNematodaNematodaNematoda

PoriferaPoriferaPoriferaPorifera

CtenophoraCtenophoraCtenophoraCtenophoraCnidariaCnidariaCnidariaCnidaria

PlacozoaPlacozoaPlacozoaPlacozoa

PlatyhelminthesPlatyhelminthesPlatyhelminthesPlatyhelminthesNemerteaNemerteaNemerteaNemertea

CiliophoraCiliophoraCiliophoraCiliophoraSarcomastigophoraSarcomastigophoraSarcomastigophoraSarcomastigophora

MicrosporaMicrosporaMicrosporaMicrosporaApicomplexaApicomplexaApicomplexaApicomplexa

MesozoaMesozoaMesozoaMesozoa

EchinodermataEchinodermataEchinodermataEchinodermata

CrustaceaCrustaceaCrustaceaCrustaceaChelicerataChelicerataChelicerataChelicerata

UniramiaUniramiaUniramiaUniramia

ProtochordatesProtochordatesProtochordatesProtochordates

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Birds MammalsReptile

Amphibian

Fish

Four Limbs

Amniotic Egg

Endothermic

Fur

Feathers

Vertebrae

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Monophyletic

• A group of all the descendants of a common ancestor

• The common ancestor is in the group

• Example: Mammalia– Ancestor was a

mammal like reptile

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Paraphyletic

• A group of descendants of a common ancestor

• Common ancestor is in the group

• Not all descendants are included

• Example: Reptiles– Does not include birds

and mammals

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Polyphyletic

• A group that has some similarities

• Common ancestor is in not in the group

• Not all descendants are included

• Example: Flying vertebrates

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*

* Archaea

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Checkpoint Questions:

1. How is information about evolutionary relationships useful in classification?

2. How are genes used to help scientists classify organisms?

3. What is the principle behind cladistic analysis?

4. Describe the relationship between evolutionary time and the similarity of genes in two species.

5. How have new discoveries in molecular biology affected the way in which we classify organisms compared with the system used by Linnaeus?