A3.2 (Classification and Cladistics)

Taxonomy

The science of classifying and naming organisms based on their characteristics and relationships.

Taxon / Taxa

A group of organisms classified as a unit in a taxonomic system; taxa is plural.

Cladistics

Method of classifying organisms based on their evolutionary relationships and shared derived characteristics.

Clade

Group of organisms consisting of a common ancestor and all of its descendants.

Cladogram

Branching diagram showing hypothesised evolutionary relationships between organisms.

Root (of a cladogram)

The common ancestral lineage from which all organisms shown in the cladogram descend.

Node

Branching point representing a common ancestor.

Terminal Branch

Branch ending in a group or organism shown at the tip of a cladogram.

Evolution

Change in heritable characteristics of populations over successive generations.

Morphology

The study of the form and structure of organisms.

Molecular Clock

Method using the rate of genetic or molecular change to estimate when organisms shared a common ancestor.

Parsimony Analysis

Method that favours the evolutionary tree requiring the fewest changes or evolutionary events.

Common Ancestor

An ancestral organism from which two or more groups evolved.

Domain

The highest taxonomic rank, consisting of Bacteria, Archaea and Eukarya.

Archaea

Domain of prokaryotic organisms that are genetically and biochemically distinct from bacteria.

Eubacteria

Domain of prokaryotic organisms commonly referred to as “true bacteria.”

Eukarya

Domain containing organisms whose cells have a membrane-bound nucleus.