cis-

1. Prefix (in italics) meaning on this side, on the near side; opposite of trans-. 2. In genetics, a prefix denoting the location of two or more genes on the same chromosome of a homologous pair, in coupling. 3. In organic chemistry (in italics), a form of geometric isomerism in which similar functional groups are attached on the same side of the plane that includes two adjacent, fixed carbon atoms ( e.g., the 2- and 3-OH groups of ribofuranose) in a ring structure. See entgegen. 4. In organic chemistry, a form of geometric isomerism with regard to carbon-carbon double bonds. Identical functional groups on the same side of the double bond are c.. When the four moieties attached to the carbons of the double bond are all different, then the E/Z nomenclature has to be followed. SYN: zusammen (1). See entgegen, zusammen. [L.]

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[L. “on this side”] a prefix denoting on this side, on the same side, on the near side.