Telomere replication, kinetochore organizers, and satellite DNA evolution.

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Abstract
Robertsonian rearrangements demonstrate 1-break chromosome rearrangement and the reversible appearance and disappearance of telomers and centromeres. Such events are quite discordant with classical cytogenetic theories, which assume all chromosome rearrangements require at least 2 breaks and consider centromeres and telomeres as immutable structures rather than structures determined by mutable DNA sequences. Cytogenetic data from spontaneous and induced telomere-telomere fusions in mammals support a molecular model of terminal DNA synthesis in which all telomeres are similar and recombine before replication and subsequent separation. This, along with evidence for a hypothetical DNA sequence, the kinetochore organizer, readily explains latent telomeres, latent centromeres and reversible (1-break) Robertsonian rearrangements. A 2nd model, involving simply recombination between like satellite DNA sequences on different chromosomes, explains not only how 1 satellite can simultaneously evolve on different chromosomes, but also why satellite DNA is usually located near centromeres or telomeres and why it maintains a preferred orientation with respect to the centromere.