Medical Definition of expression
1a: something that manifests, represents, reflects, embodies, or symbolizes something else <the first clinical expression of a disease>b (1): the detectable effect of a gene; also : the sum of the processes (as transcription and translation) by which a gene is manifested in the phenotype <gene expression can be controlled by regulatory proteins that bind to specific sites on DNA—Mark Ptashne> (2): expressivity
2: facial aspect or vocal intonation as indicative of feeling
3: an act or product of pressing out
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