The system works by placing each organism into a layered hierarchy of groups. Each group at a given layer is composed of a set of groups from the layer directly below. Therefore, in theory, one needs know only the lowest layer (species) of a particular organism in order to uniquely determine the other six layers. In practice, however, many species actually have the same species designation, so when specifiying a species, scientists use the bottom two layers - a system called binomial nomenclature.
The standard groupings (taxa) of taxonomy from most general to most specific are:
Several acronym mnemonics have been made for these, for instance King Phillip called out for good soup. Sometimes tribes, which lie between families and genera, and races, which lie below species, are also used. Intermediate ranks may be created by adding prefixes, for instance:
The term varieties is sometimes used in place of subspecies. In horticulture, it refers to populations modified by selective breeding, for instance the Peace Rose (http://www.hbssby.com/~gardener/Roses/PeaceRose.html), a hybrid Tea Rose. At the top of the scale, there has been a move towards the three domain system. The domains originally were replacements for the different kingdoms, but often count as a higher rank.
Could add a description of the difficulty in classifying microbes: their features are derived from direct visual observation, but include such procedural characteristics as Gram stain type, motility, ability to form spores, etc. However, given an unknown bacterium with a given set of characteristics, it is in general not possible to predict its phylogeny, toxicity, etc. Other methods, using genes, their DNA, and several types of RNA, are under development.
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The fruit fly so familiar in genetics laboratories is Drosophila melanogaster. Its usual classification, as well as that of humans, is as follows
| Kingdom | Animalia |
| Phylum | Arthropoda |
| Class | Insecta |
| Order | Diptera |
| Family | Drosophilidae |
| Genus | Drosophila |
| Species | melanogaster |
| Kingdom | Animalia |
| Phylum | Chordata |
| Subphylum | Vertebrata |
| Class | Mammalia |
| Subclass | Eutheria |
| Order | Primates |
| Suborder | Catarrhini |
| Family | Hominidae |
| Genus | Homo |
| Species | sapiens |
| Kingdom | Plantae |
| Division | Magnoliophyta |
| Class | Magnoliopsida |
| Order | Magnoliales |
| Family | Magnoliaceae |
| Genus | Magnolia |
| Species | acuminata |
Note in this last example, that most of the taxa are named after the type genus, Magnolia.
Taxa above the genus level are often given names derived from the type genus. The suffixes used to form these names depend on the kingdom, and sometimes the phylum and class, as follows:
| Taxon | Plants | Algae | Fungi | Animals |
|---|---|---|---|---|
| Division/Phylum | -phyta | -phyta | -mycota | |
| Subdivision/Subphylum | -phytina | -phytina | -mycotina | |
| Class | -opsida | -phyceae | -mycetes | |
| Subclass | -idae | -phycidae | -mycetidae | |
| Order | -ales | -ales | -ales | |
| Suborder | -ineae | -ineae | -ineae | |
| Superfamily | -acea | -acea | -acea | -oidea |
| Family | -aceae | -aceae | -aceae | -idae |
| Subfamily | -oideae | -oideae | -oideae | -inae |
| Tribe | -eae | -eae | -eae | -ini |
| Subtribe | -inae | -inae | -inae | -ina |
See also: