Centromere repositioning caused by activation of a neocentromere. A neocentromere may be formed de novo from a resident noncentromeric DNA on an ancestral X chromosome via epigenetic mechanisms not involving alteration to the primary nucleotide sequence of this DNA. This is then followed by the acquisition and/or amplification of repetitive DNA on the neocentromere and the inactivation and deletion of the old centromere. Alternatively, a neocentromere may be formed through the same epigenetic mechanisms following an initial transposition of a small noncentromeric genomic DNA fragment from another chromosomal site onto the ancestral X chromosome (not shown).
