Biology Chapter 26 Vocabulary

phylogeny

The evolutionary history of a species or group of related species.

systematics

A scientific discipline focused on classifying organisms and determining their evolutionary relationships.

binomial

A common term for the two-part, latinized format for naming a species, consisting of the genus and specific epithet; also called a binomen.

genus

A taxonomic category above the species level, designated by the first word of a species’ two-part scientific name.

family

In Linnaean classification, the taxonomic category above genus.

orders

In Linnaean classification, the taxonomic category above the level of family.

classes

In Linnaean classification, the taxonomic category above the level of orders.

phyla

In Linnaean classification, the taxonomic category above class.

kingdoms

A taxonomic category, the second broadest after domain.

taxon

A named taxonomic unit at any given level of classification.

phylogenetic tree

A branching diagram that represents a hypothesis about the evolutionary history of a group of organisms.

branch point

The representation on a phylogenetic tree of the divergence of two or more taxa from a common ancestor. A branch point is usually shown as a dichotomy in which a branch representing the ancestral lineage splits (at the branch point) into two branches, one for each of the two descendant lineages.

evolutionary lineage

The sequence of ancestral organisms leading to a particular taxon; represented by a branch (line) in a phylogenetic tree.

sister taxa

Groups of organisms that share an immediate common ancestor and hence are each other’s closest relatives.

rooted

Describing a phylogenetic tree that contains a branch point (often, the one farthest to the left) representing the most recent common ancestor of all taxa in the tree.

polytomy

In a phylogenetic tree, a branch point from which more than two descendant lineages emerge. A polytomy indicates that the sequence of divergence and evolutionary relationships between the descendant lineages are unclear.

cladistics

An approach to systematics in which organisms are placed into groups called clades based primarily on common descent.

clades

Groups of species that include an ancestral species and all of its descendants. A clade is equivalent to a monophyletic group.

monophyletic

Pertaining to a group of taxa that consists of a common ancestor and all of its descendants. A monophyletic taxon is equivalent to a clade.

paraphyletic

Pertaining to a group of taxa that consists of a common ancestor and some, but not all, of its descendants.

polyphyletic

Pertaining to a group of taxa that includes distantly related organisms but does not include their most recent common ancestor.

shared ancestral character

A character, shared by members of a particular clade, that originated in an ancestor that is not a member of that clade.

shared derived character

An evolutionary novelty that is unique to a particular clade.

outgroup

A species or group of species from an evolutionary lineage that is known to have diverged before the lineage that contains the group of species being studied. An outgroup is selected so that its members are closely related to the group of species being studied, but not as closely related as any study-group members are to each other.

ingroup

A species or group of species whose evolutionary relationships are being examined in a given analysis.

maximum parsimony

The principle that when considering multiple explanations for an observation, one should first investigate the simplest explanation that is consistent with the facts.

maximum likelihood

As applied to DNA sequence data, a principle that states that when considering multiple phylogenetic hypotheses, one should take into account the hypothesis that reflects the most likely sequence of evolutionary events, given certain rules about how DNA changes over time.

analogy

Similarity between two species that is due to convergent evolution rather than to descent from a common ancestor with the same trait.

orthologous genes

Homologous genes that are found in different species because of speciation.

paralogous genes

Homologous genes that are found in the same genome as a result of gene duplication.

molecular clock

A method for estimating the time required for a given amount of evolutionary change, based on the observation that some regions of genomes evolve at constant rates.

horizontal gene transfer

The transfer of genes from one genome to another through mechanisms such as transposable elements, plasmid exchange, viral activity, and perhaps fusions of different organisms.