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