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Classification and the

Tree of Life

CHAPTER 1 REVIEW

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The Tree of Life

The cell theory and the theory of evolution by naturalselection imply that all species come from preexistingspecies

all species, past and present, trace their ancestry back to asingle common ancestor.

The tree of life is a family tree of organisms that describes

the genealogical relationships among species with a singleancestral species at its base

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Speciation

a divergent process in which natural selection has causedpopulations of one species to diverge to form new species

Species

Populations of individuals which can interbreed to produce fertileoffspring

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Linnaean Taxonomy

Taxonomy is the effort to name and classify organisms.

In Linnaeus taxonomic system for classifying organisms,each organism is given a unique two-part scientific name

consisting of the genus and the species. A genus is made up of a closely relatedgroups of species.

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Taxonomic Levels Linnaeus system is hierarchical with nested taxa.

The taxonomic levels from least to most specific are as follows:

kingdom

phylum

class

order

family

genus

species

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Linnaeus

TaxonomicLevels

KINGDOM

(Animalia)

PHYLUM

(Chordata)

CLASS

(Mammalia)

ORDER

(Primates)

FAMILY

(Hominidae)

GENUS

(Homo)

SPECIES

(Homosapiens)

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How Many Kingdoms Are There? Linnaeus proposed just two kingdomsplants and animals.

However, not all organisms fall neatly into these categories.

An alternative five-kingdom system was proposed in the 1960s

Monera

Protista Fungi

Plantae

Animalia

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The Origin of the Phylogenic Tree of Life

Carl Woese and colleagues studied small subunit rRNA, as ameans for understanding the evolutionary relationships amongorganisms

(1) rRNA sequences should be very similar in closely relatedorganisms but less similar in organisms that are less closelyrelated.

(2) A phylogenetic tree reflects these relationships among species.Branches that are close to one another represent species thatare closely related; branches that are farther apart represent

species that are more distantly related.

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Changes to the Tree of Life Recent evidence indicates three major groups of organisms: One group of eukaryotesEukarya

Two groups of prokaryotesBacteria (everyday bacteria) and Archaea(extremophile bacteria)

Therefore, Woese created a new taxonomic level called the domain,consisting of

Bacteria

Archaea

Eukarya

The location of certain branches on the tree is hotly debated and theshape of the tree will continue to change as databases expand.

Which group do you

think is more

closely related to

the eukaryotic

kingdoms (yellow?)

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Phylogenetic Tree of Life

Plants, fungi, and

animals are small

branch tips on

the tree of life

This node represents the common

ancestor of archaea and eukaryotes

This node represents the common

ancestor of all organisms alive today