Figure 3 (A) Fluorescent in‐situ hybridisation (FISH) images of the Vysis^TM locus‐specific probe for chromosome 21 including D21S59, D21S341 and D21S342 on the interphase and metaphase cells of the mother. Partial karyotype of her chromosomes 21 at 550 band resolution. (B) Array comparative genomic hybridization (aCGH) profile of chromosome 21 assayed on the RPCI 19K bacterial artificial chromosome (BAC) array demonstrating duplication at megabase pairs 36–40.3. Average log₂ ratios (y axis) were plotted for all clones based on the chromosomal position (x axis), with the blue bar demarcating the centromere. Regions of normal segmental duplications are represented by blue and green triangles, and can be found at http://genome.ucsc.edu/cgi‐bin/hgGateway and http://projects.tcag.ca/variation/, respectively. Horizontal red lines indicate the log₂ ratio for each segment as segmented by circular binary segmentation.