taxonomy classifying organisms · 2007. 6. 28. · mader: biology 8 th ed. classification of living...

Mader: Biology 8th Ed.

Classification of Living Things

Chapter 20

1


Outline

• Taxonomy

– Binomial System

• Species Identification

• Classification Categories

• Phylogenetic Trees

– Tracing Phylogeny

• Cladistic Systematics

• Phenetic Systematics

• Classification Systems

2


Taxonomy

• Classification is usually based on understanding of of how organisms are related to one another through evolution.

– Natural system reflects the evolutionary history of an organism.

!Taxonomy began with Greeks and Romans.

"Aristotle

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Classifying Organisms

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Binomial System

• In mid-eighteenth century, Linnaeus developed the binomial system of naming species.– First word is genus.– Second word (specific epithet) refers to

one species within genus.!A species is designated by the full

binomial name (Genus species)."Genus can be used to refer to group

of related species.

5

Fig. 20.2a

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Species Identification

• Definition of Species

– Biological definition of a species rests on recognition that distinctive characteristics are passed from parent to offspring.

!When a species has a wide geographic range, variant types may interbreed where their populations overlap.

"Hybridization may not be indicative of different species.

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Classification Categories

• Modern taxonomists use the following classification:– Species– Genus– Family– Order– Class– Phylum– Kingdom– Domain

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Taxonomy Hierarchy

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Classification Categories

• The higher the category, the more inclusive.

• Organisms in the same domain have general characteristics in common.

• In most cases, classification categories can be subdivided into additional categories.

– Superorder

– Order

– Suborder

– Infraorder

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Phylogenetic Trees

• Systematics is the study of the diversity of organisms at all levels of organization.

– Classification lists the unique characters of each taxon and is ideally designed to reflect phylogeny.

!Phylogenetic tree is a diagram that indicates common ancestors and lines of descent.

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Classification and Phylogeny

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Phylogenetic Trees

• A primitive character is present in the common ancestor and in all members of a group.

• A derived character is one that is found only in a particular line of descent.

13


Tracing Phylogeny

• Fossil Record

– Fossil record is incomplete; thus, it is often hard to tell to which group a fossil is related.

• Homology

– Character similarity stemming from a common ancestor.

!Homologous structures are related to each other through common descent.

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Tracing Phylogeny

• Convergent Evolution

– The acquisition of the same or similar characters in distantly related lines of descent.

– Analogy

!Similarity due to convergence.

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Tracing Phylogeny

• Parallel Evolution

– The acquisition of the same or similar characters in two or more related lineages without being present in a common ancestor.

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Molecular Data

• Systematics assumes the more closely species are related, the fewer changes there will be in DNA base-pair sequences.

– Protein Comparisons

– RNA and DNA Comparisons

– Molecular Clocks

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Genetic Data

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Cladistic Systematics

• Uses shared derived characters to classify organisms and arrange taxa in a cladogram.

– Traces evolutionary history of the group under study.

!A clade is an evolutionary branch that includes a common ancestor, together with all its descendent species.

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Constructing a Cladogram

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Constructing a Cladogram

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Parsimony

• Cladists are always guided by the principle of parsimony.

– Minimum number of assumptions is the most logical.

– Cladograms are constructed leaving the fewest number of shared derived characters unexplained.

!Minimizes number of assumed evolutionary changes.

22


Phenetic Systematics

• In phenetic systematics, species are classified according to the number of their similarities.

– Ignores the possibility that some of the shared characteristics are probably the result of convergence or parallelism.

23


Traditional Systematics

• Traditional systematists mainly use anatomical data to classify organisms and construct phylogenetic trees based on evolutionary principles.

– Stress both common ancestry and degree of structural difference among divergent groups.

!Not strict in making sure all taxa are monophyletic.

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Traditional versus Cladistic View

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Classification Systems

• Until the middle of the twentieth century, biologists recognized only two kingdoms.

– Plantae (plants) and Animalia (animals)

!Protista (protists) were added as third kingdom in the 1880s.

"Whittaker expanded the classification system to five kingdoms in 1969.

# Added Fungi and Monera.

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Five-Kingdom System

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Three-Domain System

• Molecular data suggest there are two groups of prokaryotes, the bacteria and archaea, that are so different, they should be assigned to separate domains.

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Three-Domain System

• Domain Bacteria and domain Archaea contain prokaryotic unicellular organisms that reproduce asexually.– Distinguishable by a difference in rRNA

base sequences as well as plasma membrane and cell wall chemistry.!Archaea live in extreme environments.

"Methanogens"Halophiles"Thermocidophiles

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Three-Domain System

• Domain Eukarya contains unicellular and multicellular organisms whose cells have a membrane-bound nucleus.

– Sexual reproduction common.

– Contains 4 kingdoms.

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Review

• Taxonomy

– Binomial System

• Species Identification

• Classification Categories

• Phylogenetic Trees

– Tracing Phylogeny

• Cladistic Systematics

• Phenetic Systematics

• Classification Systems

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taxonomy classifying organisms · 2007. 6. 28. · mader: biology 8 th ed. classification of living...

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