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position effectPositionseffekt (ger.)

  • An effect on gene expression that depends on its chromosomal location. Genes translocated to transcriptionally active regions can have their expression increased, as happens in the Philadelphia chromosome abnormality. (Oxford Dict. of Biomedicine 2010) 

    It seems probable that such an influence of the relative position of genes on their effectiveness in development may be interpreted in terms of diffusion and localized regions of activity in the cell. This idea is, however, scarcely worth elaborating until more evidence is obtained. It may, however, be pointed out that there is another possible application of the hypothesis of a position effect.

    Sturtevant, A.H. (1925). The effects of unequal crossing over at the bar locus in Drosophila. Genetics 10, 117–147: 138.


    The senior author has now [...] obtained definitve evidence (see Muller and Prokofyeva, 1934) of the correctness of the ‘position effect’ interpretation, through the finding that different rearrangements involving the sucte locus in Drosophila in the great majority of cases result in phenotypically different ‘allelomophs’, whereas nearly identical rearrangements (scute 4 and scute L8) have given sensibly the samme ‘allelomorphs’.

    Muller, H.J., Prokovyeva, A. & Raffel, D. (1935). Minute intergenic rearrangement as a cause of apparent gene mutation. Nature 135, 253-255: 253.


    The idea of a position effect, made to save the gene concept, will also have to disappear when it is recognized that the position effect is actually identical with what was called a gene. The chromosome as a unit will be found to control normal developoment or wild type.

    Goldschmidt, R.B. (1937). Spontaneous chromatin rearrangements in Drosophila. Nature 140, 767.


    position effect A change in the phenotypic expression of a gene as a result of a change in its spatial relationship to other genes on the chromosome.

    Lincoln, R.J., Boxshall, G.A. & Clark, P.F. (1982). A Dictionary of Ecology, Evolution and Systematics: 200.