Molecular and cytogenetic analyses for 99.12, the mother of patient 99.10. A. Genotyping of the proband and parents identify a number of STS markers proximal to BP4 that are triallelic for the mother and tetra-allelic for the proband. The additional alleles suggest that the r(15) extends at least through BP4 and is present in the mother and proband. B. Log2T/R ratios for the array CGH for the proband demonstrate tetrasomy for the region between BP1-BP4 and trisomy for the region between BP4 and BP5. This is consistent with a der(15) that arose from a BP4:BP5 exchange. C. Array CGH using peripheral white blood cells from the mother indicates a slight increase in dosage for clones between BP1 and BP5 (spots 1–73). The mean log2T/R ratio was 0.108 (s.d. 0.060) compared with a mean ratio of 0.072 (s.d 0.065) (p = 0.037; two tailed unpaired t-test). For both arrays, the boxed area indicates control probes. The positions of the BAC clones used for FISH are indicated. D. Metaphase chromosomes hybridized with pcm15 (green) and BAC AC120045 (red) identifies two normal homologues and a small der(15) chromosome. E-J. Metaphase spreads hybridized with pcm15 (green) and additional BAC clones spanning the duplication regions. Most cells showed a single large signal for the pcm15 clone, suggesting the r(15) was monocentric.