| Numerous genes act to remodel and repress chromatin in heterochromatin and around euchromatic genes during development. |
| In Drosophila, relocation of a euchromatic gene near centromeric or telomeric heterochromatin often leads to its mosaic silencing. |
| Position-effect variegation results from the juxtaposition of euchromatin and heterochromatin by chromosome rearrangement or transposon insertion. |
| In contrast, the 12 essential genes known to exist within the mitotic heterochromatin of chromosome 3 have remained only imprecisely mapped. |
| On a molecular level, silenced chromatin consists of specialized heterochromatin proteins and of nucleosomes carrying deacetylated histones. |
| This phenomenon is discussed in light of a possible role of heterochromatic proteins in the process of heterochromatin underrepresentation in polytene chromosomes. |
