Figure 2.—

Model for suppression of PEV of the w^m4 allele by JIL-1 null and hypomorphic alleles. (A–C) Spreading of heterochromatic factors (solid area) in a wild-type JIL-1 background. With normal levels of pericentric heterochromatic factors present the spreading across the inversion breakpoint can reach the w gene and silence gene expression. (D–F) Spreading of heterochromatic factors (solid area) in a JIL-1 null and hypomorphic allelic background. Shaded boxes indicate the redistribution to ectopic chromosome sites of heterochromatic markers occurring in JIL-1 hypomorphic mutants. Because of the reduced levels of pericentric heterochromatic factors in the JIL-1 mutant background the spreading is attenuated and does not extend far enough from the breakpoint to silence w expression.