The FISH Technique requires fluorescent genetic probes, which have to be attached (or hybridised), to the chromosome, and then seen through a fluorescent microscope, using special filters.

The FISH method means the genes can be seen, in different colours on the chromosome. This gives a much clearer idea about what is going on, than researchers have had before.

The FISH technique is, however, expensive to use because of the price of the ’paints ‘ or probes, to the chromosomes and genes, and the necessity for special filters on the microscopes.

With the equipment that the royal free hospital researchers have, so far they are able to see 7 abnormalities in the cells of the bone marrow, at once.

The FISH technique shows the chromosomes as they appear in the cell.

The Philadelphia chromosomes have 2 have two genes on them, BCR (Rhodamine Digoxigenin) and ABL (Fitc – Biotin). These two genes are labelled with fluorescent dies, BCR in red, ABL in green.

Where the two genes fuse, they produce a yellow colour.

It is the fusion of the two genes that causes the abnormal cells to divide, when the leukaemia is active

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