Cis

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Cis is a Latin noun or prefix, meaning "on the same side [of]" or "on this side [of]". It is the opposite of trans, which means "on the opposite side".

• In chemistry, a double bond (or ring) in which the greater radical on both ends is on the same side of the bond (or face of the ring) is called cis. Compare with trans.

In the diagram on the right, both hydrogen atoms (and both fluorine atoms) are on the same side of the carbon chain. As the carbons are joined by a double bond, these cannot rotate around the molecule.

See Geometric isomerism.

• In genetics, cis- is a prefix used in terms such as "cis-regulation" to signify the co-location of two or more genes on the same chromosome of a homologous pair. The action of molecules is also described in these terms (see Cis-acting).

• In geography, placenames beginning with Cis- convey the meaning "on this side of". Examples include Ciskei (referring to the Kei River), Cisleithania (Leitha), Cisalpine Gaul (Alps), Cisjordan (the region around Jordan). The antonym is Trans-.

• In astronomy cislunar means: in outer space between the Earth and the Moon. Translunar is its antonym. Similarly, a Trans-Neptunian object is a celestial object orbiting the Sun outside the orbit of Neptune, and Cis-Neptunian objects are at or before Neptune's orbit.

• In medicine and sociology, cisgender and cissexual are the opposite of transgender and transsexual, respectively. Both describe people whose gender identity matches their physical and/or assigned sex.

• In nutrition a cis fat is an unsaturated fatty acid whose hydrogen molecules are on the same side, as opposed to an unsaturated trans fat whose hydrogen molecules are on opposite sides. The difference in shape makes cis fats less likely to congest in the bloodstream and thus less dangerous than trans fats.

• In computer software, CIS stands for Clinical Information Solution.

• In information technology, CIS stands for the Center for Internet Security.