Phylogeny

•     Traces the course of evolutionary change

•     Dendrograms = graphical representation of phylogenies

Phylogenetic Systematics

•     Willi Hennig (1966)

•     Cladistics

•     Clade

–   Group of organisms that belong to one lineage plus the common ancestor

–   Evolutionary lineage

•     Organisms are placed together that belong to the same clade

•     Based on geneology and not within group variation

Apomorphy

•     Derived character

•     Derived - different from the ancestral condition

•     Symapomorphy - shared derived characteristic

Plesiomorphy

•     Characteristic inherited unchanged from an ancestor

•     Symplesiomorphy

–   Shared ancestral characteristics

•     “Only shared derived characteristics (synapomorphies) are useful in cladistics”

Cladogram

•      Dendrogram depicting geneology, or how clades are arranged.

•      Represents an hypothesis about lineages and their evolutionary relationships

•      Primitive condition

–    ancestral state of a character

•      Derived condition

–    Descendant state after transformation

Cladistic Concepts

•     Monophyletic

•     Polyphyletic

•     Paraphyletic

Homology

•     Homologous

–   Traits that are inherited from a common ancestor

Analogy

•      Structures that perform a similar function but may or may not share a common ancestor

•      For example: bird wings and insect wings.  Both used for flight

Convergence

•      Morphological, embryological and paleotological studies have utilized phenotypes to observe underlying genetic similarities

•      Convergence = Distantly related organisms resemble each other

•      For example: octopus eye and mammalian eye

•      Analogous but not homologous structures

Homoplasy

•      Features that simply look alike

•      For example: Insects that have wings shaped like leaves

–   Do not function in photosynthesis ¹ analogous

–   Insects and plants share no common ancestor ¹ homologous

Parsimony