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Interphase FISH test for trisomy 21
The chromosome 21 probe is labelled with a red fluorochrome and a control probe (for
chromosome 18) is labelled in green. The two green dots show that the hybridization
has worked for this cell, and the three red dots show that there are three copies of
chromosome 21. The clinical report is based on examining a large number of cells. For
prenatal diagnosis a mix of differently coloured probes from chromosomes 13, 18, 21, X
and Y is often used.