Phylogeny and the tree of life

Organismal Biology

Systematics

The scientific study of the diversity of organisms and their relationships, primarily focusing on classification and evolutionary history.

Taxonomy

The science of naming, describing, and classifying organisms, reflecting their evolutionary relationships and hierarchical structure.

Classification

The orderly grouping of organisms into hierarchical categories based on similarities and evolutionary relationships.

Taxon

A group of one or more populations of organisms that form a unit in biological classification, reflecting their evolutionary relationships.

Phylogeny

The study of evolutionary relationships among biological entities, often represented as a tree.

Domain, Kingdom, Phylum, Class, Order, Family, Genus, Species

The organization of living organisms into levels of increasing specificity, from broadest groups like domains and kingdoms down to species, reflecting evolutionary relationships.

How to interpret phylogeny

tracing branch points to determine common ancestors and understanding that taxa sharing a more recent branch point are more closely related than those that diverged earlier.

Monophyletic

a lineage with a single common ancestor (a true clade)

Holophyletic

a lineage including all descendants of a single common ancestor

Parathyletic

a lineage including some but not all descendants of a single common ancestor (NOT A CLADE)

Polyphyletic

a lineage or trait found in independent lineages (NOT A CLADE)

Sister Taxa

groups that share a closest common ancestor, but are not part of each other.

Branch points

points on a phylogenetic tree that represent the divergence of two species from a common ancestor.

Rooted Trees

Phylogenetic trees that have a single ancestral lineage at the base, defining the direction of evolutionary time.

Clade

A lineage of organisms descended from a common ancestor. (contains ALL descendants from ancestor)

Grade

group of organisms that share similarity but not shared by common ancestry

Divergent evolution

evolution of homologous characteristics into new forms/phenotypes in same clade (Descent with modification)

Convergent Evolution

Evolution of analogous characteristics is distantly related clades

Homology

Similar based on shared common ancestry

Analogy

similar due to common function

Plesiomorphic

ancestral characteristic

Apomorphic

derived chacteristic

Symplesiomorphic

A shared, ancestral characteristic

Synapomorphic

A shared, derived characteristic

Autapomorphic

un shared, derived chacteristic