Phylogeny the Tree of Life Chapter 26 Phylogeny

Phylogeny & the Tree of Life Chapter 26

Phylogeny & Systematics � Phylogeny: ◦ 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)

Phylogenies show evolutionary relationships 26. 1

Taxonomy �Grouping according to evolutionary similarities �Binomial nomenclature (Linnaeus) �Domains Species �Taxon (plural: taxa): named taxonomic hierarchy ◦ Ex: Panthera is the taxon at the genus level

Phylogenetic Tree �Links taxonomy and phylogeny �Branch points ◦ Divergence of two lineages from a common ancestor �Most recent common ancestor

How to read a phylogenetic tree

Phylogenies are inferred from morphological and molecular data 26. 2

Recall: �Homology ◦ Similarities due to common ancestry �Analogy ◦ Similarities due to convergent evolution

Morphology �Physical & DNA traits and genetics are homologous in organisms with recent shared common ancestors

Molecular Systematics �Uses DNA and other molecules to hypothesize evolutionary history

Shared characters are used to construct phylogenetic trees 26. 3

Cladistics �Science of constructing a cladogram

Cladistics �Clades ◦ Groups of organisms sharing a common ancestor

Monophyletic �A 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

Polyphyletic �A 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 & Outgroup �In: Group of study (make comparisons) �Out: Group that diverged prior to ingroup

New information continues to revise our understanding of the tree of life 26. 6

A Changing Approach to Classification of Life �New evidence means continued revision of classification ◦ Genome (DNA) sequencing

Tree of Life �Current classification: ◦ Three domains � 6 kingdoms

3 Domains First life on Earth

�Tree of Life Video