Chromosome 17 epialleles. (a) Ideogram of chromosome 17 (top). Zoom inset of epialleles showing monomer number for HORs and orientation. D17Z1B HORs carry 14 monomers, as do D17Z1C HORs. D17Z1 HORs are variable in the human population, with wild type epialleles containing 16-mer, 15-mer, and 14-mer HORs (pink) and variant epialleles containing wild type HORs in addition to 13-mer and 12-mer HORs (green). (b) Variation of the D17Z1 epiallele is linked to centromere activity. When the variation in D17Z1 increases, CENP-A nucleosomes (red) decrease; when variation exceeds 80%, the centromere assembles on the D17Z1B epiallele.