Unit 6: Classification and Diversity

KEY CONCEPT Organisms can be classified based on physical similarities.

Unit 6: Classification and Diversity

Linnaeus developed the scientific naming system still used today.

• Taxonomy is the science of naming and classifying organisms.

• A taxon is a group of organisms in a classification system.

White oak:Quercus alba

Unit 6: Classification and Diversity

The Linnaean classification system has limitations.

• Linnaeus taxonomy doesn’t account for molecular evidence.– The technology didn’t exist during Linneaus’ time.– Linnaean system based only on physical similarities.

Unit 6: Classification and Diversity

• Physical similarities are not always the result of close relationships.

• Genetic similarities more accurately show evolutionary relationships.

Unit 6: Classification and Diversity

KEY CONCEPT Modern classification is based on evolutionary relationships.

Unit 6: Classification and Diversity

Cladistics is classification based on common ancestry.

• Phylogeny is the evolutionary history for a group of species.– evidence from living species, fossil record, and

molecular data– shown with branching tree diagrams

Unit 6: Classification and Diversity

• Cladistics is a common method to make evolutionary trees.

– classification based on common ancestry– species placed in order that they descended from

common ancestor

Unit 6: Classification and Diversity

• A cladogram is an evolutionary tree made using cladistics.

– A clade is a group of species that shares a common ancestor.

– Each species in a clade shares some traits with the ancestor.

– Each species in a clade has traits that have changed.

Unit 6: Classification and Diversity

• Derived characters are traits shared in different degrees by clade members.

– basis of arranging species in cladogram

– more closely related species share more derived characters

– represented on cladogram as hash marks FOUR LIMBS WITH DIGITS

Tetrapoda clade1

Amniota clade2

Reptilia clade3Diapsida clade4

Archosauria clade5

EMBRYO PROTECTED BY AMNIOTIC FLUID

OPENING IN THE SIDE OF THE SKULL

SKULL OPENINGS IN FRONT OF THE EYE & IN THE JAW

FEATHERS & TOOTHLESS BEAKS.

SKULL OPENINGS BEHIND THE EYE

DERIVED CHARACTER

Unit 6: Classification and Diversity

FOUR LIMBS WITH DIGITS

• Nodes represent the most recent common ancestor of a clade.

• Clades can be identified by snipping a branch under a node.

Tetrapoda clade1

Amniota clade2

Reptilia clade3Diapsida clade4

Archosauria clade5

EMBRYO PROTECTED BY AMNIOTIC FLUID

OPENING IN THE SIDE OF THE SKULL

SKULL OPENINGS IN FRONT OF THE EYE AND IN THE JAW

FEATHERS AND TOOTHLESS BEAKS.

SKULL OPENINGS BEHIND THE EYE

NODE

DERIVED CHARACTER

CLADE

Unit 6: Classification and Diversity

• Molecular data may confirm classification based on physical similarities.

• Molecular data may lead scientists to propose a new classification.

Molecular evidence reveals species’ relatedness.

• DNA is usually given the last word by scientists.

Unit 6: Classification and Diversity

KEY CONCEPT Molecular clocks provide clues to evolutionary history.

Unit 6: Classification and Diversity

Molecular clocks use mutations to estimate evolutionary time.

• Mutations add up at a constant rate in related species.– This rate is the ticking of the molecular clock.– As more time passes, there will be more mutations.

DNA sequence from ahypothetical ancestor

The DNA sequences from twodescendant species show mutationsthat have accumulated (black).

The mutation rate of thissequence equals one mutationper ten million years.

Mutations add up at a fairlyconstant rate in the DNA of species that evolved from a common ancestor.

Ten million years later—one mutation in each lineage

Another ten million years later—one more mutation in each lineage

Unit 6: Classification and Diversity

• Scientists estimate mutation rates by linking molecular data and real time.

– an event known to separate species– the first appearance of a species in fossil record