A genus (, genera) is a taxonomic rank used in the biological classification of living and fossil organisms in biology. In the hierarchy of biological classification, genus comes above species and below family. In binomial nomenclature, the genus name forms the first part of the binomial species name for each species within the genus.
:E.G., ''Felis catus'' and ''F. silvestris'' are two species within the genus ''Felis''. ''Felis'' is a genus within the family Felidae.
The composition of a genus is determined by a taxonomist. The standards for genus classification are not strictly codified, so different authorities often produce different classifications for genera. There are some general practices used, however, including the idea that a newly defined genus should fulfill these three criteria to be descriptively useful:
# monophyly – all descendants of an ancestral taxon are grouped together;
# reasonable compactness – a genus should not be expanded needlessly; and
# distinctness – with respect to evolutionarily relevant criteria, i.e. ecology, morphology, or biogeography; note that DNA sequences are a ''consequence'' rather than a ''condition'' of diverging evolutionary lineages except in cases where they directly inhibit gene flow (e.g. postzygotic barriers).
The term comes from the Latin ' ("origin; type; group; race"),〔(Merriam Webster Dictionary )〕 a noun form cognate with ''ラテン語:gignere'' ("to bear; to give birth to"). It probably came to Latin from the (アラビア語:''Gins'' جنس) meaning type. Linnaeus popularized its use in his 1753 ''Species Plantarum'', but the French botanist Joseph Pitton de Tournefort (1656–1708) is considered "the founder of the modern concept of genera".
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