07 Phylogenies and the History of Life

Taxonomy

The science of classifying organisms to make classification systems with each organism placed into increasingly more inclusive groupings

Linnaeus

Father of taxonomy. Replaced classification scheme of middle ages with a binomial system

The Taxonomic Hierarchy

(Did King Philip come over from Greece Saturday?) Domain, Kingdom, Phylum, Class, Order, Family, Genus, Species. Domain is most diverse, then getting to species is most specific.

Domain of eastern gray squirrel

Eukarya

Kingdom of eastern gray squirrel

Animalia

Phylum of eastern gray squirrel

Chordata

Class of Eastern gray squirrel

Mammalia

Rules for writing species names

1. genus name+ specific epithet.

2. 2) Genus name always capitalized.

3. 3) A specific epithet was never capitalized.

4. 4) Both names are italicized.

Systematics

study of the diversity of life and the evolutionary relationships between organisms. This constructs phylogenies by looking at similarities and differences between species

Cladistics

method for sorting organisms into clades based on similarity in homologous features

Shared Derived Character

newly evolved trait that is unique to a particular group

Ex: feathers, birds share them but obv u wont find them on humans

Shared ancestral character

A trait shared by the group because it was already
present in the ancestors of the group.

Ex: All vertebrates (fish, amphibians, reptiles, birds, and mammals) have a backbone, which was inherited from a common ancestor. However, since this trait is present in many different groups, it is considered ancestral, not unique to any one group.

Outgroup

Group used for comparison to assign polarity of Ancestral vs. Derived

Ex: Lancelets (small, fish-like marine animals) are an outgroup when studying vertebrates. Since they lack a backbone but share some basic features with vertebrates, they help scientists identify which traits (like a notochord) were present before vertebrates evolved.

Parsimony

simplest explanation is the best one

maximum parsimony

method used to infer evolutionary relationships by selecting the phylogenetic tree that requires the fewest evolutionary changes (mutations, trait modifications, etc.). It follows the logic that evolution tends to take the simplest path rather than introducing unnecessary complexity.

monophyletic

ALL descendants came from one common ancestor

paraphyletic

consists of an ancestral species and some, but not all, of its descendants

polyphyletic

a group that doesn't share common ancestral species

Clade

branches that come from single node

node

branch point where two or more branches come together in a tree

root

hypothesized ancestor of all organisms in tree (trees can be drawn without or with a root)

Homology

similarity due to common ancestry

analogy

similarity due to selection not ancestry, similar traits are adaptive under similar ecological/ environmental pressures

molecular phylogenies

using DNA as the trait to construct phylogenies based on genetic similarity. Understanding how many mutations occurred in each ancestor