Medical Definition of express
1: to make known or exhibit by an expression
2a: to force out by pressure <express breast milk manually or by electric pump>b: to subject to pressure so as to extract something <some pumps express one breast at a time—Paula Lynn Parks>
3: to cause (a gene) to manifest its effects in the phenotype <a gene selectively expressed in lung tumors>; also : to manifest or produce (a character, molecule, or effect) by a genetic process <individuals with the gene express symptoms of the disease> <differentially expressed proteins>
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