Systematics and Phylogeny Vocabulary

Flashcards testing core vocabulary definitions from the BIOL 108 Systematics and Phylogeny lecture.

Taxonomy

The science of naming and classifying organisms.

Nomenclature

The system of naming rules used in biological classification.

Systematics

The theory and practice of classifying organisms according to their evolutionary history (phylogeny).

Phylogeny

Depicts the evolutionary relationships among both extinct and living organisms as lines of evolutionary descent of species, organisms, or genes from common ancestors.

Phylogenetic tree

A visual representation of a hypothesis about evolutionary relationships among a set of organisms or groups of organisms called taxa.

Taxa (singular: taxon)

Organisms or groups of organisms positioned at the tips of external branches on a phylogenetic tree.

Node (Branch point)

A point on a phylogenetic tree representing the hypothetical common ancestor of the lineages descended from that point.

Speciation

The divergence of two lineages from a common ancestor, represented by branch points on a phylogenetic tree.

Root

The node representing the most recent common ancestor of all the taxa in a phylogenetic tree.

Sister taxa

Two groups of organisms that share an immediate common ancestor not shared with any other taxa, making them each other's closest relatives.

Basal taxon

A lineage that diverges early in the evolutionary history of a group, originating near the root of the tree.

Polytomy

A node on a phylogenetic tree that has three or more descendant lineages, typically indicating unresolved divergence patterns or rapid speciation.

Clade

A group consisting of a common ancestor and all its descendants, both living and extinct.

Most Recent Common Ancestor (MRCA)

The internal node representing the hypothetical shared ancestor of a specific clade.

Cladogram

A type of phylogenetic tree showing evolutionary relationships where only the branching pattern (topology) is important, with branch lengths being arbitrary.

Phylogram

A phylogenetic tree where branch lengths indicate evolutionary change, such as the number of character changes or chronological time.

Homology

Similarity between organisms due to shared ancestry and evolutionary origin.

Homologous structures

Anatomical or morphological resemblances representing variations on a structural theme present in a common ancestor.

Analogy

Similarity between organisms due to convergent evolution rather than shared evolutionary ancestry.

Convergent evolution

The process where unrelated organisms independently evolve similar traits or adaptations in response to similar environmental conditions and selective pressures.

Ingroup

The primary group of taxa whose evolutionary relationships are being studied.

Outgroup

One or more taxa related to the ingroup that diverged earlier, used as a reference point to root the tree and distinguish ancestral from derived traits.

Character

An anatomical, physiological, or molecular feature used to compare taxa in phylogenetic analysis.

Character state

The observed variations or specific values of a character used to evaluate evolutionary changes.

Cladistics

A method used to infer evolutionary relationships using homologous characters to group taxa based on shared derived characters.

Monophyletic group

A group consisting of an ancestor taxon, all of its descendants, and no other unrelated taxa (synonymous with a clade).

Paraphyletic group

A grouping that consists of a common ancestor and some, but not all, of its descendants.

Polyphyletic group

A grouping that includes distantly related taxa but does not include the most recent common ancestor of all group members.

Shared derived character (Synapomorphy)

A derived trait that evolved in the Most Recent Common Ancestor (MRCA) of a clade and is unique to that specific group.

Shared ancestral character (Symplesiomorphy)

An ancestral trait shared by taxa of a clade that originated in an ancestor preceding the MRCA of that clade.

Apomorphy

A derived character state that differs from the ancestral condition.

Plesiomorphy

An ancestral character state inherited from distant ancestors.

Maximum parsimony

An algorithmic criterion in tree-building that selects the phylogenetic tree requiring the fewest evolutionary changes.

Maximum likelihood

An algorithmic method for tree construction that considers the statistical probability of specific evolutionary changes, such as genetic mutations.