Ch. 26 Vocab

Phylogeny and the Tree of Life

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

paraphyletic

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

basal taxon

in a specified group of organisms, a taxon whose evolutionary lineage diverged early in the history of the group

homologs

a pair of chromosomes of the same length, centromere position, and staining pattern that possess genes for the same characters at corresponding loci. One homologous chromosome is inherited from the organism’s father, the other from the mother.

polyphyletic

pertaining to a group of taxa that includes distantly related organisms but does not include their most recent common ancestory

phylogeny

the evolutionary history of a species or group of related species

family

in Linnaean classification, the taxonomic category above genus

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

kingdom

a taxonomic category, the second broadest after domain

homoplasy

a similar (analogous) structure or molecular sequence that has evolved independently in two species

taxonomy

a scientific discipline concerned with naming and classifying the diverse forms of life

orthologous genes

homologous genes that are found in different species because of speciation

genus

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

taxon (plural, taxa)

a named taxonomic unit at any given level of classification

sister taxa

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

class

in Linnaean classification, the taxonomic category above the level of order

shared derived character

an evolutionary novelty that is unique to a particular clade

order

in Linnaean classification, the taxonomic category above the level of family

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

cladistics

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

polytomy

in a phylogenetic tree, a branch point from which more than two descendant taxa emerge. Indicates that the evolutionary relationships between the descendant taxa are not yet clear.

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

monophyletic

pertaining to a group of taxa that consists of a common ancestor and all of its descendants. This taxon is equivalent to a clade.

branch point

the representation on a phylogenetic tree of the divergence of two or more taxa from a common ancestor. 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.

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.

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. It 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.

analogous

having characteristics that are similar because of convergent evolution, not homology

ingroup

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

clade

a group of species that includes an ancestral species and all of its descendants. Equivalent to a monophyletic group.

phylogenetic tree

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

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

domain

a taxonomic category above the kingdom level. Consists of Archaea, Bacteria, and Eukarya.

A discrete structural and functional region of a protein

analogy

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

systematics

a scientific discipline focused on classifying organisms and determining their evolutionary relationships

paralogous genes

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

maximum parsimony

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

specific epithet

the second part in a binomial; unique for each species within the genus 

scientific name

is described by binomial consisted of a genus and specific epithet

homologies

Phenotypic and genetic similarities due to ancestry

Convergent evolution

when different taxa/species solve a problem in the same way evolutionarily. This examines analogous structures.

Divergent evolution

the process by which an ancestral characteristic becomes adapted to new roles. This examines homologous structures

gene families

result of repeated gene duplications

transformation

the process by which a cell in culture acquires the ability to divide indefinitely, similar to the division of cancer cells; or a change in genotype and phenotype due to the assimilation of external DNA by a cell. When the external DNA is from a member of a different species, transformation results in horizontal gene transfer.