Medical Definition of marker
: something that serves to identify, predict, or characterize <a surface marker on a cell that acts as an antigen>: asa: biomarker <The recent discovery of a serological marker for the hepatitis C virus has greatly improved diagnostic accuracy for this form of hepatitis.—Gary P. Wormser, letter in The Journal of the American Medical Association, 12 June 1991>b: genetic marker <The idea in genetic linkage analysis is to see if any particular marker, which serves as a signpost for a specific region of a chromosome, is consistently inherited along with the disease …—Leslie Roberts, Science, 29 Jan. 1993>—called also marker gene
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