Position-effect variegation

The position effect variegation ( PEV ) is a phenomenon in genetics.

Discovery

Hermann Muller, Nobel Prize for Medicine in 1946, described in 1930 the model organism Drosophila melanogaster a " variegated " ( means something like " multi-colored " or " colored " ) chromosome Mutationsphänotyp after X-ray irradiation.

This phenomenon has been referred to as position effect variegation. It opened the experimental method for the isolation and molecular analysis of genes that heterochromatic chromatin and gene silencing control. In the PEV euchromatic gene regions heterochromatisiert variable after relocation to a new locus in proximity to constitutive heterochromatin, ie decommissioned variable. The classic example is the Drosophila w [ m4 ] ( ie white- mottled -4) mutant. In this mutation, the white gene is brought into the vicinity of pericentric heterochromatin by an inversion of the X chromosome. Normally, the white gene is expressed in every cell of the Drosophila eye, which leads to a phenotype with red eyes. In Drosophila the w [ m4 ] mutation eye color is a red and white mosaic, thus " multicolored ", " colorful " or even variegated in English. In a proportion of the cells, the white gene, which is responsible for the eye color in Drosophila heterochromatisiert.