7.1 Phylogenetic Relationships

Phylogeny

The evolutionary history of relationships among organisms.

Phylogenetic Tree

"Diagram showing evolutionary history and relationships between species

Lineage

Series of ancestor–descendant populations through time.

Node

"Represents a splitting event: speciation (species tree)

Root

The common ancestor of all species/taxa in the tree.

Cladogenesis

One species splits into two or more distinct species (branching evolution). Increases biodiversity.

Anagenesis

Gradual evolution of a single lineage without branching. Species changes over time but does not split.

Taxon

"Any named group of species (e.g.

Clade

A taxon including a common ancestor and all its descendants. True evolutionary grouping.

Sister Species / Clades

Two species or clades that are each other’s closest relatives.

Characters

"Heritable traits used to reconstruct phylogenies (morphology

Shared Character

Trait two lineages have in common.

Derived Character

"A new trait unique to a lineage

Shared Derived Character (Synapomorphy)

"Derived trait shared by members of a clade

Homologous Traits

"Traits inherited from a common ancestor (e.g.

Analogous Traits

Similar traits that evolved independently (convergent evolution). Example: bat and bird wings as wings.

Evolutionary Reversal

"Reversion of a derived trait back to the ancestral state (e.g.

Homoplasies

"Similar traits due to convergent evolution or reversals

Ingroup

Group of primary interest in building a phylogeny.

Outgroup

"Related group outside the ingroup

Parsimony Principle

The simplest tree (fewest evolutionary changes/homoplasies) is preferred.

Maximum Likelihood Modeling

Statistical method to identify the most likely phylogeny given DNA sequence data.

Monophyletic Group

A clade containing a common ancestor and all descendants. Correct grouping in classification.

Paraphyletic Group

Group containing a common ancestor but not all its descendants.

Polyphyletic Group

Group that does not include the most recent common ancestor of its members. Misleading grouping.

Molecular Clock

"Uses constant rates of genetic mutations to estimate divergence times. Requires calibration (fossil record

Radiometric Dating

Dating rocks using half-life decay of radioactive isotopes.

Stratigraphy

"Dating based on layering of rocks/sediments

Applications of Phylogenetic Analysis

"Reconstruct past events

Linnaean Classification

"System created by Carl Linnaeus (1707–1778). Uses binomial nomenclature: Genus + species (e.g.

Phylogenetic Classification

Modern system based on evolutionary history. Only clades (monophyletic groups) should be named.