Figure 6.

Position effect variegation of the white gene in Drosophila. The upper chromosome and eye are wild-type. The lower chromosome has an inversion that placed the white gene next to constitutive heterochromatin (black bar), resulting in a mottled eye. The red bar indicates a boundary that normally prevents the spread of silencing. (Reprinted from Elgin SC, Reuter G. 2013. Cold Spring Harb Perspect Biol 5: a017780, doi:10.1101/cshperspect.a017780, Fig. 1A, p. 4, © Cold Spring Harbor Laboratory Press.)