Chapter 26 – Phylogeny & the Tree of Life

26.1

Phylogeny Evolutionary history of a species or a group of

related species Made by using evidence from systematics

Focuses on classifying organisms & relationships Uses fossils, morphology, genes, & molecular

evidence

Taxonomy Ordered division of organisms into categories Based on a set of characteristics used to assess

similarities & differences

BinomialNomenclature

2 part naming system that consists of the GENUS & the SPECIES

Example: Canis familiaris (common dog)

Devoloped by Linnaeus

Hierarchical classification of organisms:

DOMAIN

KINGDOM

PHLUM

CLASS

ORDER

FAMILY

GENUS

SPECIES

The level of relatedness increases as you move down the list

Phylogenetic trees Used to depict hypotheses about evolutionary

relationships The branches of the trees reflect the

hierarchical classifications of groups nested within more inclusive groups

26.2

Phylogenies are inferred from morphological & molecular data

1) Homologous structures Similarities due to shared ancestry (whale’s

flipper)

2) Convergent evolution When 2 organisms developed similarities as they

adapted to similar environmental challenges Note due to common ancestor

Streamlined bodies of a tuna & dolphin

3) Analogous structures Structures from convergent evolution Wings of butterfly & bat

4) Molecular systematics Uses DNA to determine evolutionary

relationships The more alike the DNA sequences of 2

organisms, the more closely related they are

26.3

Building of a phylogenetic tree

A cladogram depicts patterns of shared characteristics among taxa & forms the basis of a PT

A clade (within a tree) is defined as a group of species that includes an ancestral species & all of its descendants

A valid clade is monophyletic, signifying that it consists of the ancestor species and all its descendants

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

A polyphyletic grouping consists of various species that lack a common ancestor

26.4

The rate of evolution in DNA sequences varies from one part of the genome to another

By comparing the different sequences, one can investigate relationships between groups of organisms that diverged a long time ago

DNA that codes for mitochondrial DNA evolves rapidly Used to explore recent events

DNA that codes for ribosomal RNA changes relatively slowly Useful for investigating relationships between

taxa that diverged hundreds of millions of years ago

Molecular clocks Methods used to measure the absolute time of

evolutionary change Based on the observation that some genes

appear to evolve at constant rates

Difficulties of molecular clocks The molecular clock does not run as smoothly

as neutral theory predicts Irregularities result from natural selection in

which some DNA changes are favored over others

Estimates of evolutionary divergences older than the fossil record have a high degree of uncertainty

The use of multiple genes may improve estimates

26.6

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

Early taxonomists classified all species as either plants or animals

Later, five kingdoms were recognized: Monera (prokaryotes), Protista, Plantae, Fungi, and Animalia

More recently, the three-domain system has been adopted: Bacteria, Archaea, and Eukarya

The three-domain system is supported by data from many sequenced genomes

Bacteria & Archaea Contain prokaryotic organisms

Eukarya Contain eukaryotic organisms

Characteristic

Bacteria Achaea Eukarya

Nuclear Envelope No No Yes

Membrane-bound Organelles

No No Yes

Introns No Yes Yes

Histone proteins used with DNA

No Yes Yes

Circular chromosome

Yes Yes No