BioConcepts

expressionExpression (ger.)

• The appearance in a phenotype of a character or effect attributed to a particular gene; also, the process by which possession of a gene leads to the appearance in the phenotype of the corresponding character. (OED 2011)
  category gene

  1927

  I use the word “manifestation” to signify the presence of the given character in the phenotype of the fly, and the word “expression” to signify the degree and form of the character. […] Some cases of strong hereditary variations of the expression of radius incompletus […] enable us to suppose that a great hereditary variability of the phenotypic expression of this gene could be obtained with the aid of a more precise accounting.

  Timoféeff-Ressovsky, N.W. (1927). Studies on the phenotypic manifestation of hereditary factors, I. On the phenotypic manifestation of the genovariation radius incompletus in Drostophila funebris. Genetics 12, 128-198: 131; 157.

  1930

  the physiology of gene expression

  Schultz, J. (1930). A spectrophotometric study of the pigments in the eye-color mutations of Drosophila. Science 72, 406-407: 406.