Chapter 25: Phylogeny and Systematics

“Taxonomy is the division of organisms into categories based on… similarities and differences.” p. 495, Campbell & Reece (2005) Shown is a phylogenetic tree

Fossils are preserved remnants of organisms that lived in the past Fossils form in sedimentary rock, the oldest fossils in the lower strata and younger on the upper strata Fossil record is incomplete and favors larger organisms, those with hard bodies or parts, those that were abundant and widespread. Fossil Record

 Fossils

Homology- similarity due to common ancestry (same structure different function): wing of bat, arm of human, flipper of whale Analogy- similarity due to convergent evolution ( same function different structure) :two kinds of moles  Morphological Evidence

 Analogies These “moles” only look similar Placental Marsupial

Computers are used to analyze DNA sequences for homologous nucleic bases. Molecular Evidence

 Taxonomic Categories Did (Domain) Karen’s (Kingdom) Pups (Phylum) Chew (Class) On (Order) Fuzzy (Family) Grey (Genus) Squirrels (Species)

 Binomial Nomenclature  Example: Escherichia coli, E. coli, Escherichia spp.,  The genus name (Escherichia) is always capitalized and comes first  The species name (coli) is never capitalized  The species name is never used without the genus name  The genus name may be used without the specific epithet  Both genus and species names are always underlined or italicized  Genera may be abbreviated, e.g., the E. in E. coli,

 Cladistics  Cladistics is a technique by which organisms are assigned to different (monophyletic) taxa  Cladistics works by grouping together organisms such that within taxa individuals share more homologies than they do with individuals found in different taxa  Cladistics also rejects the inclusion of similarities... …that result from convergent evolution (i.e., analogies) …that are homologies that are shared with other taxa (i.e., shared primitive characteristics)

 Classifying Clades Each deeper branch point represents greater divergence

Classifying Proper Clades: Passing the Test A clade consists of an ancestral species plus all descendant species Here is a missed ancestor species

 Monophyletic A correct grouping A clade Ancestor All descendants

 Paraphyletic This is missing descendant species

 Polyphyletic Convergent evolution? Polyphylies happen when species are included in “clades” that they don’t belong in

 Convergent Evolution  Polyphyletic taxa occur as a consequence of mistaking analogies for homologies  Analogies result from convergent evolution: the two species do similar things in similar environments so evolve similarly  The key difference between an analogy and a homology is: The common ancestor between the two species will lack the common structure

 Analogies

 Shared Derived Characters SDC

Cladogram based on Shared Derived Characteristics. An outgroup is a species that is related to the species being studied (ingroup), but less closely related

 Molecular Clocks The molecular clock is a yardstick for measuring absolute time of evolutionary change based on the observation that some genes and other regions of genomes seem to evolve at constant rates Neutral theory states that much evolutionary change in genes and proteins has no effect on fitness It states that the rate of molecular change in these genes and proteins should be regular like a clock

Phylogenetic analysis shows that HIV is descended from viruses that infect chimpanzees and other primates Comparison of HIV samples throughout the epidemic shows that the virus evolved in a very clocklike way Applying a Molecular Clock- The Origin of HIV

The tree of life is divided into three great clades called domains: Bacteria, Archaea, and Eukarya 1- last common ancestor of all living things 2. ancestor of eukaryotic cells 3. symbiosis of mitochondrial ancestor 4. symbiosis of chloroplast ancestor Universal Tree of Life