Phylogeny & the Tree of LifeChapter 26

Phylogeny & SystematicsPhylogeny:

◦ Evolutionary history of a species or group of species◦ Determined by evidences from fossil record, homologous

structures, molecular homologies Systematics:

◦ Helps us understand phylogeny (data analysis of phylogeny)

26.1Phylogenies show evolutionary relationships

TaxonomyGrouping according to

evolutionary similaritiesBinomial nomenclature

(Linnaeus)Domains SpeciesTaxon (plural: taxa):

named taxonomic hierarchy◦Ex: Panthera is the taxon

at the genus level

Phylogenetic TreeLinks

taxonomy and phylogeny

Branch points◦Divergence of

two lineages from a common ancestor

Most recent common ancestor

How to read a phylogenetic tree

26.2

Phylogenies are inferred from morphological and molecular data

Recall:Homology

◦Similarities due to common ancestryAnalogy

◦Similarities due to convergent evolution

Morphology & DNAPhysical traits and genetics are

homologous in organisms with recent shared common ancestors

Molecular SystematicsUses DNA and other molecules to

hypothesize evolutionary history

26.3

Shared characters are used to construct phylogenetic trees

CladisticsScience of constructing a

cladogram

CladisticsClades

◦Groups of organisms sharing a common ancestor

MonophyleticA valid clade is

monophyletic, it consists of the ancestor species and all its descendants

Paraphyletic

A paraphyletic clade consists of an ancestral species and some, but not all, of the descendants

PolyphyleticA

polyphyletic clade includes many species that lack a common ancestor

Species Change Over Time (Nodes)

Characteristics Shared primitive

character ◦ Homologous structure

that is older than the branching of a particular clade from other members of that clade

◦ It is shared by more than just the taxon we are trying to define.

◦ Example – mammals all have a backbone, but so do other vertebrates.

Characteristics

Shared derived character ◦ New evolutionary

feature, unique to a particular group

◦ Example - all mammals have hair, and no other animals have hair.

Ingroup & OutgroupIn: Group of study (make

comparisons)Out: Group that diverged prior to

ingroup

26.6

New information continues to revise our understanding of the tree of life

A Changing Approach to Classification of LifeNew evidence means continued

revision of classification◦Genome (DNA) sequencing

Tree of LifeCurrent

classification:◦Three domains

6 kingdoms

3 Domains

First life on Earth

Tree of Life Video