A3.2 Classification and Cladistics

A3.2.1. Classification system

Why do we have them?

1. Info storage & retrieval: so many org. and more to come: so much knowledge; need systems to store so much info

2. Identification; to find species name by going down chain → subgroups

3. Predicitve value: species in a group share traits; characteristics are predictabl

4. Researching origins: share traits many traits come from certian ancestor → evolutionary origins of species??

A3.2.2 Disadvantages of traditional taxa hierarchy

Taxa = groups used to classify DKPCOFGS, one group = taxon

Why not good?

1. can be unclear when to group vs. nongroup

2. can be disagreements on which species in which group

3. can be difficult to say whether a difference is a family or genus or etc…

4. hybrids….?

Bc. of gradual diverging of species. Not 1 moment speciation

A3.2.3 Classifying using evolutionary relationships

Phylogeny: study evolutionary past using molecular DNA structures → phylogenetic tree: show evol. relations: family tree but then of just species.…

Clade = monophyletic group: group with all its common ancestors and descendants

A3.2.4 Clade = common ancestry

clade = group of organisms evolved from same common ancestor. Splits at speciation.

A3.2.5 Evolutionary Molecular Clock

On cladogram; show when speciation happened.

Can figure out by viewing nr of different base sequences per unit years…

We know mutation rate so we figure out how long.

A3.2.6/7 Constructing & Using cladograms

Branching diagram representign ancestor-descendant relationships.
Its all hypotheses, open for testing and falsificaiton.

Cladogram = morphological traits
Phylogenetic tree = genetic relationships

Node = place where speciation event happened
Outgroup = group furthest related: furthest node away…
Sister group = closest tg.
Root = base of cladogram: common ancestor to all species
Terminal branch = most specific; most recetly evolved

A3.2.8 Cladistics & reclassification

Can both confirm or indicate that they’re in the wrong groups. Eg. reclassification of figwort family, and other flowering plants.

A3.2.9 3-domain-classification

Eubacteria - Archae - Eukarya

Archaea: single celled org. distinct from bacteria, very okd. Extreme conditions: hydrothermal vents; extremophiles

Eubacteria: bacteria.

Eukarya: all other life: single celled to whales…: has nucleus and organelles

Used to be just prokaryotes and eukaryotes, but now bacteria vs archae+eukarya