Studies of transcriptional gene silencing in Drosophila melanogaster suggest that most of chromosome 4 resembles pericentric heterochromatin. However, some modifiers of position-effect variegation, including chromosome 4 dosage and loss of SU(VAR)3-9, have different effects on silencing in pericentric vs. distal arm chromosome 4 heterochromatin, distinguishing these two heterochromatin types.
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