Possible model for the decondensation of juxtacentromeric heterochromatin in jumping translocations of 1q. A spectrum of 1qh decondensations occur in MM cells, ranging from an apparently normal 1qh region (A), to slightly elongated 1qh (B), or highly decondensed and thread-like 1qh (C). Partial endoreduplication of 1q apparently occurs while heterochromatin is decondensed (D). Fusions with telomeres of nonhomologous chromosomes may be facilitated by the highly decondensed heterochromatin (E). The origin of a new derivative chromosome with 1q fused to telomere (F). Condensation of heterochromatin on derivative chromosome (G) creates the appearance of a typical whole-arm jumping translocation.