Chapter 25: Phylogeny and Systematics Phylogeny = the evolutionary history of a species Systematics = study of biological diversity in an evolutionary context / reconstructing phylogeny

I. Fossil Record and Geologic Time

A. Fossils Usually in sedimentary rock and the hard stuff remains Sometimes minerals seep in and replace tissue Sometimes thin films Sometimes casts Trace Fossils Sometimes they die and don’t decompose

B. Dating Fossils 1. Relative Dating - gives a general idea of time line - use sediment layers - Precambrian, Paleozoic, Mesozoic, Cenozoic - separated by mass extinction

Video

B. Fossil Dating 2. Absolute Dating - defines periods in years - radiometric dating – measures radioactive isotopes - half-life - ex. Carbon 14, Uranium L amino acids vs D amino acids 3. Fossils leave an incomplete record

C. Continental Drift and Phylogeny Drifting of continents leads to speciation Forming (250 million years ago) and breaking up (180 million years ago) of Pangaea

D. Mass Extinction Fossils show long periods of gradual action and then huge species turnover Permian Mass Extinction – between Paleozoic and Mesozoic / 90% of marine life died Cretaceous Mass Extinction – between Mesozoic and Cenozoic / maybe a comet, firestorm, and volcanoes There is a creative side to destruction

II. Systematics: Connecting Classification to Phylogeny

A. Hierarchical System of Classification

1. Binomial Nomenclature Genus species Examples: Homo sapien Drosophila melaganster Canis lupus Borellia burgdorferia

2. Hierarchical Classification Domain, Kingdom, Phylum, Class, Order, Family, Genus, Species Taxon – taxonomic unit Phylogenic tree – based on taxonomic grouping

Phylogenic Tree

B. Phylogenic Systematics - Classification based on evolutionary history - Use fossil records, assess relationships, compare anatomy, DNA

1. Clades Clade – evolutionary branch in a cladogram (phylogenic tree) Cladogram – phylogenic diagram based on cladistics Based on 2 way branching points Each point represents a divergence from a common ancestor Monophyletic – ancestral species and descendants (same as clade) Paraphyletic – ancestor and some, not all, of its descendents Polypyletic – lacks a common ancestor

Cladogram (phylogenic tree)

2. Constructing a Cladogram

a. Homology vs. Analogy Homology – likeness attributed to shared ancestry Analogy – similarities due to convergent evolution More homology = closer relationship

b. Identify Shared Derived Characters (Traits) Shared Primitive Characters – homology common to a group more inclusive then others / ancestral / backbone in mammals Shared Derived Characters – unique to a clade / hair in mammals

c. Perform Outgroup Comparison Way to differentiate from derived and primitive characters Outgroup – species closely related to the species being studied but less closely related to any of the study group members (ingroup) Ingroup – organisms being studied Based on idea that homologies present in ingroups and outgroups are primitive and were present in a common ancestor

Cladistic Taxonomy

3.Phylogeny from Molecular Data Compare genes by comparing DNA sequences (proteins) and align the sequences for comparison

4. Parsimony Nature should be the simplest explanation consistent with the facts

5. Phylogenic Trees are Hypotheses

Some parts of the genome evolve at a constant rate Graph the percent different in sequences vs. time / AIDS 6. Molecular Clocks