One who expresses or conveys ideas, feelings, or information; something that serves to express or manifest.
From 'express' (Latin expressus, 'pressed out') plus the suffix '-or' meaning 'one who does the action.' The term evolved to mean anything that communicates or makes something evident.
In molecular biology, an 'expressor' is a gene that's actually working and producing protein—it's the opposite of a dormant gene, making it a key concept in understanding how DNA actually functions in living cells.
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