A3.2- Classification and Cladistics

The 3 Domains

1. Domain Bacteria

2. Domain Archaea

3. Domain Eukarya

The 6 Kingdoms

• Eubacteria

• Archaebacteria

• Animalia

• Plantae

• Fungi

• Protista

Traditional taxonomy levels (taxa)

• Domain

• Kingdom

• Phylum

• Class

• Order

• Family

• Genus

• Series

Criteria to determine if classification is based on evolutionary relationships

1. Every organism evolved from a common ancestor is in the same taxonomic group

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

Clade

A group of organisms evolved from a common ancestor based on shared criteria

Clades include:

• Alive species

• Dead species (granted they evolved from the common ancestor)

Cladogram

A branching diagram that represents ancestors / descendant relationships

Molecular evidence

• Comes from base sequences of genes / amino acid sequences of proteins

• Is most accurate in determining evolutionary history

• Particularly useful with fossils

Molecular clock

The larger number of sequence differences between two species, the longer since they diverged from a common ancestor

Base or amino acid sequences as the basis for cladograms

Recent common ancestors:

• Have few differences

• Closer related

Less recent common ancestors:

• Many differences

• Distantly related

Terminal branch

Ends that represent individual clades

Nodes

Branching points of a cladogram

Root

The base of the cladogram. The hypothetical common ancestor of all the clades

Reclassification of organism

Happens when the species placed in a taxonomic group do not all share a common ancestor, or species that evolved from the same ancestor have been placed in different groups