The science of organizing and categorizing living organisms into classes called taxa
Systematics
The study of the diversification of life forms over time, both past and present, and their relationships between other species
Both a systematist and a taxonomist provide: scientific names, detailed descriptions of organisms, collect and keep volumes of specimens, offer classifications for the organisms
However, it is the systematist that investigates on evolutionary histories and considers environmental adaptation of species
Taxonomic classification (Linnaean system)
Uses a hierarchical model
Moving from the point of origin, the groups become more precise until the branch terminates as a single species
Phylogeny
The study of relationships and their evolutionary development among different groups of organisms
The more distant the relationship between two related species, the farther back in time they shared a common ancestor
Phylogenetic tree (tree diagram)
Basal taxon - lineage that evolved early from the root that remains unbranched
Sister taxa - two lineages stemming from the same branch point
Polytomy - branch with more than two lineages; it serves to illustrate where scientists have not definitively determined all of the relationships
Although sister taxa and polytomy do share an ancestor, it does not mean that the groups of organisms split or evolved from each other
Cladistics
A method of hypothesizing relationships among organisms, established by Willi Hennig in the 1950s
Cladogram
A diagram showing evolutionary relationships within one or more clades
Monophyletic group (clade)
A collection of organisms that include an ancestor species and all of their descendants
Can be separated from the root with a single cut
Paraphyletic group
Needs two or more cuts to separate from the root
Polyphyletic group
Needs two or more cuts to separate from the root
Grouping 1 in Figure 9 is monophyletic, grouping 2 is paraphyletic, and grouping 3 is polyphyletic
DNA molecules are long chains of nucleotides twisted into a double helix shape.