 For Class I, the proposed mechanism is that chromatid breakage occurs during mitosis, resulting in a chromosome fragment.That acentric chromosome fragment may segregate with the intact chromatid and result in partial tetrasomy; or, it may segregate with the complementary broken chromatid and result in partial trisomy because the broken chromatid may be saved by telomere restitution.In both cases, the inverted duplicated marker forms only after cell division and replication by rejoining the broken, replicated ends of the fragment.