Table 1 FISH probes used in the study

1

chr21 centromeric probe (proximal to both duplications)

D21Z1 (Cytocell, Cambridge, UK)

red

2

probe overlapping the proximal duplication

RP11-482O14 (BlueGnome, Cambridge, UK)

orange

3

probe at the proximal end of the segment between the duplications

RP11-45 M19 (Source BioScience, Nottingham, UK)*

green

4

probe at the distal end of the segment between the duplications

RP11-64I20 (Source BioScience)*

blue

5

probe overlapping the distal duplication

RP11-134 K3 (Source BioScience)*

red

6a (6b)

DSCR1 (or chr21qter subtelomere) probe (distal to both duplications)

PN21 (Kreatech Diagnostics, Amsterdam, The Netherlands) (or D21S1575 (Cytocell))

red