A3.2 Classification and Cladistics

Taxon?

classification group eg phylum

Taxonomy

assigning organisms to groups

Difficulties classifying organisms into the traditional hierarchy of taxa

Often can be disagreements over the taxonomic ranks allocated to a new species.

Such uncertainty comes from the gradual divergence of species over time.

E.g. species diverge to the point there is enough diversity for the genus to split.

Eukaryote classification

Kingdom

Phylum

Class

Order

Family

Genus

Species

Advantages of classification corresponding to evolutionary relationships

In each taxonomic group, all the species are evolved from the same common ancestor.

If this criteria is satisfied all the members of the taxonomic group will share traits that they have inherited. These shared traits are called synapomorphies

The sharing of traits between members of a taxonomic group allows biologists to make predictions based on classification.

Clades as groups of organisms with common ancestry and shared characteristics

Cladograms are tree diagrams where each branch point represents splitting of two new groups form a common ancestor.

Each branch point, (node), represents a speciation event by which distinct species are formed via divergent evolution.

The fewer nodes between two groups the more closely they are related.