1 Classification. 2 Why Classify? To study the diversity of life, biologists use a classification...

Classification

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.

Aristotle 384 BC

• Classified organisms as either plants or animals

Carolus Linnaeus 1707-1778

• Classification system• Based on physical

structure• Taxonomic groups of

related organisms• Binomial nomenclature

(two names ex.Homo sapiens)

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

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”

Taxonomic Groups

Classification of Man

• Kingdom Animalia

• Phylum Chordata

• Class Mammalia

• Order Primates

• Family Hominidae

• Genus Homo

• Species Homo sapiens

Species

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

• Reproductively isolated group

Ernst Mayr

Different Species

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?

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

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.

Cladogram

• Evolutionary relationship of a group of organisms

• Each clad (group) share something in common

• Ancestral traits are the oldest

• Derived traits evolved later

Cladogram for Transportation

• Wheels are the most ancestral

• Wings are the most derived

Construct a Cladogram

Gorilla

• Four limbs• Fur• Lost tail

• Four limbs• Fur• Tail

Lizard

• Four limbs• Tail

• Tail

Chimpanzee

• Four limbs• Fur• Lost tail

Clad With 4 Limbs

Clad With Fur

Clad With No Tail

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

Gorilla Chimpanzee

Lizard

Four Limbs

Tail Lost

Gorilla Tail?

• How do we know the gorilla lost its tail?

Gorilla’s Vestigial Tail

Gorilla Human

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:

• 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.

• 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

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

Phylogenetic Tree

• Shows evolutionary relationships

• More historical than cladogram

MyxozoaMyxozoaMyxozoaMyxozoa

ArthropodaArthropodaArthropodaArthropoda AnnelidaAnnelidaAnnelidaAnnelida

MolluscaMolluscaMolluscaMollusca

LophophoratesLophophoratesLophophoratesLophophorates

HemichordataHemichordataHemichordataHemichordata

ChordataChordataChordataChordata

Other Other pseudocoelomatespseudocoelomates

NematodaNematodaNematodaNematoda

PoriferaPoriferaPoriferaPorifera

CtenophoraCtenophoraCtenophoraCtenophoraCnidariaCnidariaCnidariaCnidaria

PlacozoaPlacozoaPlacozoaPlacozoa

PlatyhelminthesPlatyhelminthesPlatyhelminthesPlatyhelminthesNemerteaNemerteaNemerteaNemertea

CiliophoraCiliophoraCiliophoraCiliophoraSarcomastigophoraSarcomastigophoraSarcomastigophoraSarcomastigophora

MicrosporaMicrosporaMicrosporaMicrosporaApicomplexaApicomplexaApicomplexaApicomplexa

MesozoaMesozoaMesozoaMesozoa

EchinodermataEchinodermataEchinodermataEchinodermata

CrustaceaCrustaceaCrustaceaCrustaceaChelicerataChelicerataChelicerataChelicerata

UniramiaUniramiaUniramiaUniramia

ProtochordatesProtochordatesProtochordatesProtochordates

Birds MammalsReptile

Amphibian

Four Limbs

Amniotic Egg

Endothermic

Feathers

Vertebrae

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

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

Polyphyletic

• A group that has some similarities

• Common ancestor is in not in the group

• Not all descendants are included

• Example: Flying vertebrates

* Archaea

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?

1 Classification. 2 Why Classify? To study the diversity of life, biologists use a classification...

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